Senecioneae (Asteraceae) of the Succulent Karoo and “geography of macroevolution of higher plants”: a chorological essay

The geographic characteristic of plant macroevolution is manifested in general in neither even, nor random distribution of the archaic and advanced representatives of a higher taxon in its range. The explanatory concepts proposed are still contradictory. Besides, they are poorly testable, because they concern too long-time intervals during which multiple major changes in both the environment and the ranges of taxa can have occurred; these changes usually continue untraceable in fossil records. The tribe Senecioneae in the Succulent Karoo is best suited for studying the geographic patterns of plant macroevolution for the following reasons: i) the environment of the Succulent Karoo has resulted from unidirectional climate change over 10 million years (accordingly, large fluctuations of the taxon ranges there are highly unlikely); ii) the phylogeny of the tribe Senecioneae is quite fully recognized (and it is not distorted by extinctions, at least at the level of genera); iii) Senecioneae are completely allochthonous in the Succulent Karoo (accordingly, interpretation of results becomes easier and simpler). The archaic genera of Senecioneae are as numerous in the Succulent Karoo as the highly advanced ones, whereas the mid-advanced genera are completely absent there. Such a genus composition of the tribe in the area concerned cannot be explained by the cradle and museum concept, since this area is outside of center of origin/diversification of Senecioneae. The zonal stratification concept is inapplicable to this case, since the climate of the Succulent Karoo was changing unidirectional all the time without noticeable fluctuations. All other concepts proposed are also inapplicable, as they treat the emerging of archaism gradient(s) in the taxon range, but not a deficiency/absence of mid-advanced representatives of a higher taxon in a territory occupied by its archaic and highly advanced members. The absence of mid-advanced members of Senecioneae in the Succulent Karoo could be explained as follows. Any higher taxon very rarely and at long time intervals acquires traits that enable it to spread to areas which greatly differ in their environments from the center of origin/diversification of this taxon. All new subordinate taxa that originate during these time intervals remain confined in the center of origin/diversification of the higher taxon. Accordingly, only archaic and most advanced representatives of this higher taxon would be found faraway its center of origin/diversification.

Summary.The geographic characteristic of plant macroevolution is manifested in general in neither even, nor random distribution of the archaic and advanced representatives of a higher taxon in its range.The explanatory concepts proposed are still contradictory.Besides, they are poorly testable, because they concern too long-time intervals during which multiple major changes in both the environment and the ranges of taxa can have occurred; these changes usually continue untraceable in fossil records.The tribe Senecioneae in the Succulent Karoo is best suited for studying the geographic patterns of plant macroevolution for the following reasons: i) the environment of the Succulent Karoo has resulted from unidirectional climate change over 10 million years (accordingly, large fluctuations of the taxon ranges there are highly unlikely); ii) the phylogeny of the tribe Senecioneae is quite fully recognized (and it is not distorted by extinctions, at least at the level of genera); iii) Senecioneae are completely allochthonous in the Succulent Karoo (accordingly, interpretation of results becomes easier and simpler).The archaic genera of Senecioneae are as numerous in the Succulent Karoo as the highly advanced ones, whereas the mid-advanced genera are completely absent there.Such a genus composition of the tribe in the area concerned cannot be explained by the cradle and museum concept, since this area is outside of center of origin/diversification of Senecioneae.The zonal stratification concept is inapplicable to this case, since the climate of the Succulent Karoo was changing unidirectional all the time without noticeable fluctuations.All other concepts proposed are also inapplicable, as they treat the emerging of archaism gradient(s) in the taxon range, but not a deficiency/absence of mid-advanced representatives of a higher taxon in a territory occupied by its archaic and highly advanced members.The absence of mid-advanced members of Senecioneae in the Succulent Karoo could be explained as follows.Any higher taxon very rarely and at long time intervals acquires traits that enable it to spread to areas which greatly differ in their environments from the center of origin/diversification of this taxon.All new subordinate taxa that originate during these time intervals remain confined in the center of origin/diversification of the higher taxon.Accordingly, only archaic and most advanced representatives of this higher taxon would be found faraway its center of origin/diversification.Senecioneae (Asteraceae) Суккулентного Кару и «география макроэволюции высших растений»: хорологическое эссе А. К. Тимонин 1 , Л. В. Озерова 2 , Р. К. Эбервайн 3 1 Московский государственный университет им.М. В. Ломоносова, Ленинские горы, д. 1(12), г.Москва, 119234, Россия   2 Главный ботанический сад им.Н. В. Цицина РАН, ул.Ботаническая, д. 4, г.Москва, 119234, Россия   3 Региональный музей Каринтии, ул. Либерогассе, д. 6, г. Клагенфурт, 9020, Австрия Ключевые слова: аллохтонная флора, биогеография, градиент архаичности, зональная стратификация, концепция «колыбель и музей», оттесненные реликты, правило прогрессии, центры происхождения, экваториальная помпа, Юго-Западная Африка.

Interpretations within dispersal biogeography
The patterns of distribution of archaic and advanced representatives of a higher taxon within its area were most often analyzed within the framework of dispersal biogeography and explained by specific localization of macroevolutionary transformations of their body plans (Jablonski, 1993).Two explanations for the observed phenomenon have been suggested.Senecioneae (Asteraceae) of the Succulent Karoo and "geography of macroevolution of higher...

Progression rule explanation
The so-called progression rule has been formulated (originally as Progressionsregel) (Hennig, 1950(Hennig, , 1960(Hennig, , 1966) ) within phylogenetic biogeography which is dating back to Darwin's views (Crisci, Katinas, 2009).According to this rule, the formation of a new taxon is initiated by the expansion of the range of the original taxon and the settlement of its representatives in territories with different environment.When adapting to this environment, they become more and more different from their ancestral species and transform into new species (Darwin, 1872).The now prevailing cladistics proclaims that the origin of every new species at the periphery of expanded area implies that the members of its ancestral species that stayed in the original area are also changed into a new species (Hennig, 1966).Meanwhile, the environment in the original area has hardly changed, if at all.Accordingly, the new species having formed there is only minimally different from the ancestral one (Hennig, 1950;Zunino, Zullini, 2010).Resultantly, evolving higher taxon tends to accumulate its minimally changed archaic representatives in its original area whereas its advanced representatives successively originate at the periphery of its expanding area (Fig. 1); the further from the center of origin of a higher taxon, 1 the more advanced are its members (Hennig, 1950(Hennig, , 1966;;Brundin, 1972;Morrone, Crisci, 1995;Morrone, 2009;Zunino, Zullini, 2010;Looney et al., 2016;Zhirkov, 2017).
The inference that most of higher taxa originate in tropics and spread later towards higher latitudes is in a good agreement with the paleontological data (Thorne, 1977;Kafanov, 1987;Meyen, 1987b;Doyle et al., 1990;Zherikhin, 1992;Jablonski, 1993;Harnik et al., 2010;Jablonski et al., 2013;Brown, 2014;Coiro et al., 2019).It is a cornerstone of both Darlington's (1957) out-of-the-tropics concept and Meyen's (1987a) equatorial pump concept3 (Fig. 3).The emerging new taxa replace the more archaic representatives of their embracing higher taxon to result not only in ousting of these archaic members towards the high-latitude periphery of the area of embracing taxon but in extraequatorial persistence of the archaic forms (Meyen, 1987b), this persistence being the longer the further from the equatorial zone they dwell.

Causes of the extraequatorial persistence of archaics
Many taxa managed to spread from the tropics they had arisen to high latitudes in their lifespan (Ross, 1988;Jablonski et al., 2013).As the advanced representatives of a taxon emerge in some time lag after the archaic ones, they arrive at high latitude areas also in some time lag to result in latitude positive gradient of archaic forms and their extraequatorial persistence (Wallace, 1876a;Geptner, 1936).However, the potential rate of species expansion is very high (see Eskov, 1984;Sauer, 1988).Therefore, successive emergences and expansions of more advanced members of a taxon would facilitate the latitudinal positive gradient of archaic forms only of lower taxa, viz. the species and perhaps also the genera (Timonin, 2011), while this gradient is also found in taxa of a higher ranks (Darlington, 1957;Meyen, 1987b;Chernov, 1988;Jablonski, 1993).
Not all taxa emerging in the tropics move to higher-latitude areas.Most middle rank taxa emerging within the tropics stay therein (Stehli et al., 1969;Chernov, 1988;Leighton, 2005;Jablonski et al., 2006Jablonski et al., , 2013;;Arita, Vásquez-Domínguez, 2008;Krug et al., 2008;Harnik et al., 2010;Brown, 2014) either due to purely stochastic processes (Arita, Vásquez-Domínguez, 2008), or because they are unable to develop adaptations to the extratropical climates (Chernov, 1988;Harnik et al., 2010;Brown, 2014;Azovsky et al., 2016) 4 .Therefore, the archaic representatives of a higher taxon gradually accumulate in the tropics as the more advanced ones emerge (Jablonski et al., 2006(Jablonski et al., , 2013)).The tropics are thus both the cradle for new forms of the higher taxon and the museum5 which preserves its archaic representatives (Gaston, Blackburn, 1996;Mordkovich, 2005;Jablonski et al., 2006Jablonski et al., , 2013;;Moreau, Bell, 2013).The archaic forms of the higher taxon do not actually displace towards the extratropical periphery of its area (Jablonski et al., 2006), so the latitudinal archaism gradient of the higher taxon should be attributed to the fact that the diversity of its archaic forms decreases much slower with the latitude than the diversity of its advanced forms.Some deficiency of the advanced forms of a higher taxon is resultantly observable at high lati- Senecioneae (Asteraceae) of the Succulent Karoo and "geography of macroevolution of higher... tudes (Chernov, 1988;Mordkovich, 2005;Jablonski et al., 2006Jablonski et al., , 2013)).
The outlined cradle and museum concept implicitly assumes the universal and essentially unidirectional orthogenetic narrowing of the adaptive capabilities of a higher taxon in the course of its evolutionary advancing, the assuming seeming highly questionable.In addition, the fact that the high-latitude decreasing of the diversity of advanced forms of a higher taxon hardly affects it's the most advanced members is unexpected and inexplicable within the framework of this concept (Chernov, 1978).

Interpretations within contracting area reasoning
Both Progressionsregel and diversity pump concepts are completely dispersal; they accordingly reason the taxon archaism gradient with expansion of taxon areas.However, the development of the taxon areas is equally affected by their expansion and contraction (Geptner, 1936;Wulff, 1944;Van der Spoel, 1983;Eskov, 1984;Newman, Foster, 1987;Leighton, 2005;Arita, Vásquez-Domínguez, 2008;Jablonski et al., 2013;etc.).Contractions of the taxon areas have also been named as the major, if not the only reason for the latitudinal archaism gradients within higher taxa.

Inverse latitudinal archaism gradient
The latitudinal archaism gradient of avian tribes (Gaston, Blackburn, 1996) and families of woody dicotyledons (Kerkhoff et al., 2014) has been attributed to the contraction of their areas and their relocation to lower latitudes caused by Late Tertiary and Quaternary cooling in the high latitudes and succeeded by recolonization of high latitudes with the subsequent climate warming.Contractions of their areas were total, but recolonizations of high latitudes turned out selective: only advanced representatives of higher taxa were able to recolonize high latitudes, as they considerably surpassed the archaic forms as regards to their colonizing potential (Gaston, Blackburn, 1996;Kerkhoff et al., 2014).Resultantly, archaic representatives of higher taxa are now concentrated in the tropics, while evolutionary advancement and youth of their representatives increase with the latitude (Fig. 4).Thus, latitudinal archaism gradients are inverse in these taxa as regards to mostly ones described in biogeography (Gaston, Blackburn, 1996).These inverse latitudinal gradients of taxon archaism have been concluded from the modern distribution of the taxa concerned.So, these gradients characterize just the present distribution of archaic and advanced representatives of these taxa.Such a distribution could be a short-term pattern which could show the specifics of area transformations during periods of rapid (as compared to the rate of evolutionary processes) climate fluctuations, the pattern being principally different from the geographic modes of macroevolution under long-term, rather stable abiotic environment (Emeljanov, 2004).
Such an evenness of the environment is thought to have resulted in that centers of origin/diversification of the higher taxa were scattered disorderly on the Earth, the taxon archaism gradients were numerous and multidirectional, and not only higher taxa but also very many lower-rank ones were cosmopolitan (Eskov, 2008).The thermal gradient on the Earth began to grow from the mid-Tertiary due to high-latitude cooling and contemporal warming in the subequatorial (tropical sensu stricto) zone (Razumovsky, 1971(Razumovsky, , 1999;;Zherikhin, 1978;Valentine, 1984;Newman, Foster, 1987;Raymond et al., 1989;Newman, 1991;Eskov, 1994Eskov, , 2008)).The area of the formerly global climate and areas of taxa adapted to that climate contracted to the modern subtropical zones; accordingly, the new biotas of more advanced forms emerged within the equator zone as well as in temperate and high latitudes, where the climate significantly changed (Zherikhin, 1978;Eskov, 1994Eskov, , 2008)).The latitudinal archaism gradient resultantly became two-directional, viz.from the equator to the subtropics and from the poles to the subtropics.
Resumptive concept and its drawbacks Increasing of latitudinal thermal contrast is a long-term but transitory transformation of the Earth's climates.Epochs of clear latitudinal zones of climate alternate with epochs of a globally equalized warm (subtropical) climate.Accordingly, the regimes of zonal stratification and equatorial pump, which determine the geographic pattern of macroevolution, also alternate (Eskov, 1994(Eskov, , 2008)).
While there is now a general consensus regarding past cardinal changes of the Earth's climates, but the existence of globally equalized subtropical climates during the Phanerozoic which is a sine qua non prerequisite for the zonal stratification, is highly contestable (Hayek, 1926;Chernov, 1988;Emeljanov, 2004;etc.).Warming and cooling of climates were often accepted to be global against the background of maintained steep latitudinal thermal gradient (see Chumakov, 1993) 9 .Climate transformations of this kind resulted in irregular shifts, widening, and narrowing of climate zones, and also in appearance and disappearance of the polar climate (Hayek, 1926;Geptner, 1936;Fischer, 1960;Chernov, 1975;Gladenkov, 1995;Kafanov, Kudryashov, 2000;Leighton, 2005;Jansson et al., 2013;etc.).Those climate transformations must have been accompanied by appropriate changes of taxa areas.However, no such changes in taxon areas could result in concentration of their archaic representatives precisely in subtropical zones.

Test model
The fact that macroevolutionary processes are geographically structured (Jablonski, 1993) seems to be taken for granted.Nevertheless, any concrete distribution patterns of archaic and advanced representatives of higher taxa as well as the causes of these patterns have been described variably.These disagreements are possibly attributable to the diversity of the taxa per se (Buzas, 1972;Jablonski, 1993;Fig. 5. Bidirectional archaism gradient; zonal stratification concept.More gray means more archaism.Senecioneae (Asteraceae) of the Succulent Karoo and "geography of macroevolution of higher... Gage, 2004;Leighton, 2005;Rolland et al., 2014) or to differences in geographic patterns of macroevolution at different levels of the taxonomic hierarchy (Emeljanov, 2004).Since all biogeographical patterns are of statistical nature (Jablonski et al., 2013), then further studies of geographic distribution of both archaic and advanced representatives of various higher taxa are required to distinguish between spatial-temporal patterns of macroevolution and mere statistical deviations10 .

Model selection
As a matter of fact, the current area of any modern taxon can be revealed in much detail.However, observed current areas of taxa are a result of their expansion and regional extinction (Wulff, 1944;Darlington, 1957;Leighton, 2005;Jablonski et al., 2006;Jansson et al., 2013;etc.)which could have happened repeatedly in many cases (Jablonski et al., 2006).The temporal dynamics of taxon areas can be reconstructed on the base of their modern distribution, but such reconstructions are fraught with gross mistakes if not checked against paleontological data (Liebermann, 2002;Jablonski et al., 2006;Eskov, 2008) 11 .
The application of paleontological data for reconstructing dynamics of taxon areas is also highly restricted due to their limited availability and fragmented nature (Haeckel, 1866;Liebermann, 2002).Of Phanerozoic organisms, there are only all classes of skeletal invertebrates (Prothero, 2013), many orders of vascular plants (Meyen, 1987a), and probably also all families of terrestrial tetrapods (Chernykh, 1986;Kalmar, Currie, 2010) that seem to be represented as fossils.On contrary, some 90 % of the total species and genera did not leave any trace in the paleontological record (see Foote, Raup, 1996) 12 .This makes our knowledge of the areas of higher taxa that include these genera and species certainly incomplete; moreover, the extent of this data gap can hardly be accurately estimated.Even when fossils are preserved, they merely evidence the existence of a certain taxon at a certain time in certain site, but they do not allow us to assess confidently the whole taxon area, let alone its temporal changes (Hayek, 1926;Zunino, Zullini, 2010;Jablonski et al., 2013;Zullini, 2018).Therefore, the paleobotanists are doomed to operate with more or less justified reconstructions even when collecting paleobiogeographical data (Makridin, Meyen, 1988).
In addition, the use of paleontological data to study the geographical patterns of macroevolution is hampered by the fact that the time sequence of the appearance of representatives of higher taxa in the fossil record often does not correspond to the sequence of their actual appearance (Morrone, 2009).Moreover, many characters of organisms are lost in course of their fossilization to result in that rather many fossil genera as well as taxa of other ranks are really paraphyletic groups (Foote, Sepkoski, 1999), thereof the usability of such taxa for studying geographic patterns of macroevolutionary processes further decreases (Brundin, 1972;Parenti, Ebach, 2009;Ladiges et al., 2012).
The above discussion clearly shows that special selection of a model object is necessary for studying geographical features of macroevolution when working either with neontological or with paleontological data.

Suggested perspective
Biogeographic patterns are inextricably linked with the ecological ones (Simpson, 1953a;Morrone, 2009) and are ultimately reduced to the latter13 (Valentine, 1969;Wiens, Donoghue, 2004;Brown, 2014;Azovsky et al., 2016).Whatever been interpreted, the latitudinal archaism gradient of higher taxa, which has been catching biogeographers mind for a century and a half, shows the manner the taxa colonize regions that are very different ecologically from the centers of taxon origin/diversification.Along with the well-known latitudinal ecological gradient, there is also a gradient of aridity in the tropical (in a broad sense) zone (Fischer, 1960;Brown, 2014).This aridity gradient is coincided by the diversity gradient quite similar with the latitudinal diversity gradient (Fischer, 1960;Wiens, Donoghue, 2004;Brown, 2014).The arid diversity gradient obviously also shows the manner the taxa colonize the territories that sharply differ ecologically from the center of taxon origin/diversification, where the archaic rep-resentatives of taxa can also accumulate (Cowling, Hilton-Taylor, 1999); therefore, the arid diversity gradient is also suitable for studying the geographical patterns of macroevolution.

Senecioneae of Succulent Caroo as a test model
During the expedition work in Southern Africa, Lyudmila V. Ozerova realized that the recent flora of Senecioneae in the Succulent Karoo could serve a promising model object for study of geographical patterns of macroevolution.

Succulent Karoo as a perspective region
The Succulent Karoo (Fig. 6) stretches from NNW to SSE as rather long belt in western Republic of South Africa and extreme (south)western Namibia (Jürgens, 1991;Hilton-Taylor, 1996;Mucina et al., 2006).This area has been constantly connected with (modern) Africa since the Proterozoic; it has never been completely covered by the sea since the mid-Jurassic and has therefore been retained land-based connections with the rest of southern Africa since then (Meadows, Watkeys, 1999).Therefore, plant migrations thereto from neighboring territories must have significantly prevailed over long-distance dispersal.Accordingly, the long-distance dispersal must have hardly affected the formation of the modern terrestrial biota of the Succulent Karoo, if any.Then, this accidental and unverifiable (Parenti, Ebach, 2009) dispersal can be safely ignored as a factor of development of Succulent Karoo flora.
The climate of the Succulent Karoo is the most arid variant of the South African Mediterranean climate with regular, total, albeit weak winter rains and summer drought (Hilton-Taylor, 1996;Desmet, Cowling, 1999;Burke, 2004;Mucina et al., 2006;Verboom et al., 2009), with fogs as significant factor of maintaining the humidity regime.This climate began to form about 10 mya in the Middle Miocene (Goldblatt, Manning, 2002;Verboom et al., 2009) and was completely formed by the early Pliocene 5 mya (Goldblatt, Manning, 2002;Mucina et al., 2006;Verboom et al., 2009) or perhaps even later, about 3 mya (Linder, 2005).Thus, the duration of the existence of this climate is quite comparable with the average duration of the existence of species and is much shorter than the average duration of the existence of genera (4 and 12 million years, respectively) of animals (Alekseev et al., 2001), whereas taxa of higher plants of the same ranks are considered even more long-lived (Vassiliev, 1965).Therefore, traceless extinctions of taxa are unlikely to have taken place during the formation of the modern flora of the Succulent Karoo (see also : Goldblatt, Manning, 2002;Linder, 2005) 14 .Added to that is a great stability of climate of the Succulent Karoo during the Pliocene and even Pleistocene (Goldblatt, 1997;Goldblatt, Manning, 2002;Van der Niet, Johnson, 2009).Some characters of Pleistocene climate fluctuations are clearly discernible only in the eastern border regions of the Succulent Karoo (Meadows, Watkeys, 1999; Mucina et al., 2006;Potts et al., 2013).However, even in these regions, the climate fluctuations caused just fragmentation of species areas in mountainous terrains and fluctuations of area boundaries within about 100-kilometer distance, while not a single species seems to have got locally extinct in the Succulent Karoo and re-colonized it (Potts et al., 2013).
Thus, the composition and initial distribution of the species of flowering plants that settled the Succulent Karoo seem to be quite fully detectable in the modern flora of this region.This makes it possible to use this recent flora to analyze the geographic patterns of macroevolution.

Composition and genesis of the flora of Senecioneae in the Succulent Karoo
Consideration of recent flora has an advantage over the study of paleontological material, since it Timonin A. C. et al.Senecioneae (Asteraceae) of the Succulent Karoo and "geography of macroevolution of higher... makes it possible to most fully and accurately take into account the composition and distribution of taxa.In addition, it also makes it possible to study areas of low-rank higher taxa, whose distribution most clearly manifest their ecological specificity, whereas the connection between the area of a taxon and its ecological features is significantly "blurred" for families and is virtually imperceptible for orders and higher-ranked taxa (Chernykh, 1986;Roy et al., 1996).However, the primitive low-rank taxa are extremely difficult to be distinguished from the advanced ones.That is why we follow Platnick ( 1981) and take early-divergent and late-divergent taxa (as nested in cladogram) for substitutes of archaic and advanced taxa, respectively.
The Succulent Karoo adjoins from the north and northeast to the Fynbos region, with which it is most closely associated floristically (Gibbs Russell, 1987;Jürgens, 1991;Hilton-Taylor, 1996;Cowling, Hilton-Taylor, 1999).Both regions are so similar floristically that they are sometimes combined into a Greater Cape Floristic Region (Jürgens, 1991;Mucina et al., 2006;Verboom et al., 2009;Potts et al., 2013).It is noteworthy that the Fynbos flora is generally represented by much more ancient supra-generic taxa (Cowling, Hilton-Taylor, 1999;Verboom et al., 2009).Consequently, the flora of the Succulent Karoo should be recognized as a depleted aridized derivative of the Fynbos flora (Verboom et al., 2009) and, more broadly, of the Cape flora (Cowling, Hilton-Taylor, 1999).
Asteraceae are one of the main constituents of the flora of the Succulent Karoo (Gibbs Russell, 1987).It is represented by almost 100 genera there and is second only to Mesembryanthemaceae (= Aizoaceae) in such taxa (Hilton-Taylor, 1996) 15 .Senecioneae, one of the largest tribes in family Asteraceae, is monophyletic (Pelser et al., 2007;McDonald-Spicer et al., 2019).Phylogenetic relations between its genera and species groups have been revealed in sufficient detail (Pelser et al., 2007).This makes this tribe quite usable for testing concepts on geographic patterns of macroevolution.
All the genera mentioned are the most diverse outside the Succulent Karoo.This fact and the recent emergence of this biome indicate that the centers of origin/diversification of these genera were located outside the Succulent Karoo in the Great Cape Floristic Region, the flora of the latter having been mainly formed in situ (Fenner et al., 1997).As the Succulent Karoo is the most aridized area of this Region, then settling of the concerned genera there should be considered a colonization of extreme (arid) habitats by some their species.
Since the Succulent Karoo biome has recently emerged in situ, the composition of the genera of Senecioneae therein probably demonstrates a minimally distorted sequence of the colonization of this area by differently advanced genera.Therefore, the data obtained are suitable for considering the basic concepts of the geography of macroevolution.

Geography of macroevolution as evidenced by the case study of Senecioneae of the Succulent Karoo
The Senecioneae of the Succulent Karoo has shown that the early-divergent (archaic) and the late-divergent (most advanced) genera are the most successful in colonization of the extreme arid biotopes, while the deficiency of mid-advanced ones is clearly detectable there.Other biotopes can also be extreme for a higher taxon, because the initial ecological specifics of the taxon determine which environment is extreme for it (Geptner, 1936;Gibert, Deharveng, 2002;Wiens, Donoghue, 2004;Zavarzin, 2012).Such habitats are also occupied mostly by the archaic and the most advanced representatives of higher taxa as evidenced by many taxa of flowering plants of high latitudes and high altitudes (Mazurenko, Khokhryakov, 1984); Hexapoda of polar deserts (Chernov, 1978); fresh-water Isopoda (Hessler, Wilson, 1983); synanthropic Insecta (Zherikhin, 1978); deep-sea Teleostei (Rass, 1959).Nobody knows yet how widespread is the phenomenon of the colonization of extreme habitats predominantly by archaic and most advanced representatives of a higher taxon, but it is certainly not unique to the Senecioneae of the Succulent Karoo.This phenomenon appears to be a fairly general pattern of the geography of macroevolution.
The flora of Senecioneae of the Succulent Karoo has almost certainly descended from the Cape flora of higher latitudes, which looks like sharp contradiction to the phytospreading from the equatorial region adopted in both out-of-the-tropics concept and equatorial pump one.However, both concepts ultimately attribute the evolutionary advancing (= progressive semophilesis) in the tropics to the presence of the most favorable environment there, which makes possible the existence of more numerous populations, more taxa, greater variety of selection vectors (Zarenkov, 2017), weakened selective control over the structure of organisms (Vtorov, Drozdov, 1978;Rasnitsyn, 1989;etc.).
The region of the Cape flora is similar to the Succulent Karoo in terms of thermal conditions, but it is more humid.It is thus a region with more favorable environments.Therefore, the spreading of Senecioneae genera descendant from the Cape ancestors into the Succulent Karoo is a colonizing of pessimal/ extreme habitats by them which is quite comparable with the colonizing thermally pessimal higherlatitude habitats by the taxa of tropical origin.The discrepancy between our data and the predictions of the out-of-the-tropics and equatorial pump concepts reflects the different localization of optimal and pessimal biotopes in which different taxa evolve.This discrepancy is purely geographical in nature, while there is no controversy between them in terms of biological causality.
The equatorial pump concept implies a continuous action of its machinery.More and more advanced representatives of a higher taxon constantly originate in the center of its origin under characteristically favorable environments.Emerging representatives competitively replace their more archaic predecessors and gradually spread from the center of origin of the taxon to regions with pessimal conditions and exclude archaics on their ways.Temporal lag in the colonization of regions outside the center of origin of the taxon by its advanced forms results in a centrifugal archaism gradient and long-term persistence of archaic forms far away from the center of taxon origin (this is essentially a complete reproduction of Wallace's (1876a) reasoning).However, our Timonin A. C. et al.Senecioneae (Asteraceae) of the Succulent Karoo and "geography of macroevolution of higher... data show no archaism gradient in the Great Cape Floristic Region.Instead, the early-divergent (archaic) and late-divergent (advanced) genera are represented in equal proportions (ca.45.5 % for either) in the pessimal Succulent Karoo, while the midadvanced ones are nearly absent.Acute deficiency of the mid-advanced forms there must be caused by some factor that prevents them from spreading out of the center of diversification of the higher taxon.
Just the out-of-the-tropics concept in its cradle and museum version implies that the majority of subordinate taxa which emerge within the center of diversification of their embracing higher taxon never leave this center and that only some few of them spread beyond the center limit (Stehli et al., 1969;Leighton, 2005;Jablonski et al., 2006Jablonski et al., , 2013;;Krug et al., 2008).Hence, the deficiency of the advanced forms of a taxon develops in the regions that are pessimal/extreme for this taxon (Chernov, 1978;Kafanov, Kudryashov, 2000), which manifests itself as a centrifugal gradient of increasing archaism.However, the deficiency of just the mid-advanced forms in pessimal/extreme habitats, as evidenced by the Senecioneae of the Succulent Karoo and some other cases, is by no way explicable within the framework of either out-of-the-tropics concept or its cradle and museum version.

Corrected model of geography of macroevolution: a suggestion
Some amendments in the concept of geography of macroevolution are thereof necessary as follows (Timonin, 2011).
Any higher taxon, like a species, is maximally adapted to a certain range of environments alias the adaptive zone of a taxon (Simpson, 1953b, as restricted by Van Valen, 1971).These environments define the area of ecological optimum for this taxon, in which it diversifies in course of time.A higher taxon can forever remain in the area of its ecological optimum, in spite of it can continue diversifying and advancing evolutionary therein; or else, a taxon, as it evolves, can develop an organization that will allow its members to adapt to the environment beyond its ecological optimum.Having thus evolved, the taxon would expand its adaptive zone and become able to spread to areas outside its diversification center, the areas where the environment was pessimal/extreme for it.Any evolutionary transformation causes temporal unbalancing of the adaptive compromise organization of living beings and inevitably diminishes their fitness; the more profound is the transformation, the stronger is decreasing of the fitness (Ras-nitsyn, 1989).Accordingly, evolutionary transformations are mostly feasible under reduced selection pressure (Meyen, 1987b).The pessimal/extreme environment causes additional selection pressure.That is why the pessimal/extreme environment makes therefore possible only some minimal changes of the organization of living beings, while any drastic changes are eliminated; such environment virtually preserves the evolved organization (Timonin, 2011;Grandcolas, Trewick, 2016).Hence, speciation is still possible in pessimal/extreme habitats, though it is much impeded (Jansson et al., 2013), but any significant changes of the original organization of living beings are efficiently eliminated and the appearance of more advanced members of the higher taxon is effectively hampered therein.
The adaptive compromise is looser within the area of the ecological optimum of a higher taxon (= center of taxon diversification) and selection control over the organization of living beings is reduced (Rasnitsyn, 1989).More significant restructuring of the organization and progressive semophilesis become accordingly possible within the taxon in such area.Evolutionarily advancing does not always allow emerging subordinate taxa to develop adaptations to pessimal/extreme environments (Timonin, 2011).Semophyletic advancing usually limits opportunity for adapting to pessimal/extreme habitats (Chernov, 1988) and cause the advanced representatives of a taxon remain "locked" within the (ecologically optimal) center of taxon diversification.Such a limitation is by no means permanent.Subsequent evolutionary advancing can over time result in an organism structure that would be adaptable to pessimal/extreme environment and thus would make it possible for the most advanced at that time members of the taxon to spread outside its diversification center.The "diversity pump" would still be functional, but as any pump, it would work in batch and from time to time "push out" the most advanced representatives of higher taxon away from the center of its diversification 17 .
Successive pumping out of taxon members from the diversification center is likely to be intermittent by time intervals sufficiently long for subordinate taxa to be significantly transformed 18 .Such advanced forms would be quite different from their archaic counterparts not only in taxonomic characters but also in their reactions to the environment and ways of adaptation to pessimal/extreme environments.These differences would cause that when populating pessimum/extreme areas, the advanced representatives of a higher taxon are more likely to co-exist with, not exclude the archaic ones that had settled therein earlier (Timonin, 2011).As a result, the higher taxon would be represented by its primitive and most advanced members in habitats which are pessimal/extreme for this taxon.
The emerging more advanced forms of a higher taxon would either exclude their archaic counterparts in the center of diversification of this taxon, as the Darlington's (1957) diversity pump concept and the Meyen's (1987a) equatorial pump concept proclaim, or they would partition an adaptive zone of this taxon (Simpson, 1953a) and coexist with the archaics therein, as the Gaston, Blackburn's (1996) cradle and museum concept proclaims.In the latter case, a higher taxon would accumulate its archaic representatives in its diversification center 19 .
Repeated 'pumping out" the most advanced forms of a higher taxon from the center of its diversity would result in a gradual accumulation of less and less archaic representatives of this taxon in the pessimal/extreme areas and filling the gap between the archaic and the most advanced forms therein.However, as such "pumpings out" are likely to be separated by long lapses of time, then, the less and less archaic forms of a higher taxon would accumulate in its pessimal/extreme areas at a rather low rate and the contrast between its variously advanced representatives therein would also decrease slowly and become conspicuous only in very long-term pessimal/extreme areas.Sharp contrast between differently advanced representatives of a higher taxon would be inherent in young biomes of ecologically pessimal/extreme regions, where (relatively) significant representation of archaic and most advanced forms concurs with clear deficiency of mid-advanced ones.This is exactly the situation observed in the flora of Senecioneae in the Succulent Karoo and also in the fauna of Hexapoda in Arctic deserts (Chernov, 1978).
Most taxa feature their centers of diversification near the Equator (Darlington, 1957;Kafanov, 1987;Meyen, 1987b;Jablonski, 1993;Harnik et al., 2010;Jablonski et al., 2013;Brown, 2014;etc.).Accordingly, the centrifugal gradients of the increasing archaism of representatives of higher taxa take the form of Poleward latitudinal gradients (the further from the Equator, the more archaic forms).If the center of differentiation of a higher taxon is located differently, then the archaism gradient of its representatives still remains centrifugal, but it must inevitably deviate from the Poleward latitudinal direction.Therefore, even the archaism gradient in birds and arboreal dicotyledons directed towards the Equator (Gaston, Blackburn, 1996;Kerhoff et al., 2014), i. e. opposite to the prevailing direction, cannot be considered a refutation of either out-of-the-tropics and equatorial pump concepts without additional confirmation.
Successively emerging more advanced forms of a higher taxon are undoubtedly unequal in their dispersal and adaptive capabilities to colonize the ecologically pessimal/extreme areas of this taxon.These different capabilities would geographically be expressed in different rate and distance of their spreading out of the center of taxon diversification.If a form with especially large dispersal and adaptive abilities arises at some point in time, it would be able to inhabit areas located much further from the center of differentiation of its embracing taxon than those populated by its more archaic predecessors.If the latter ones are replaced in the center of higher taxon differentiation by subsequent advanced forms, then the archaic representatives of a higher taxon would take areas outside of the center of taxon differentiation and just between those occupied by more advanced representatives (Fig. 8).We do not assert that the concentration of archaics in the subtropics and the predominance of more advanced forms of higher taxon in the equatorial zone and higher latitudes (Zherikhin, 1978;Eskov, 1994Eskov, , 2008) ) are just such a case.But we believe it is quite possible, that the location of archaic representatives of a higher taxon between its advanced ones could 19 The accumulation of archaic representatives of a higher taxon at the center of its diversification may in fact be illusory.The archaic taxa are known to settle mountains, sea depths, and other very specific 'marginal' habitats which are often smallsized and ephemeral (Geptner, 1936;Belyaev, 1966;Lemée, 1967;Birstein, 1985;Erwin, 1985;Newman, 1991;Eskov, 1994;Gibert, Deharveng, 2002;Van Dover et al., 2002;Ricklefs, 2005;Moreau, Bell, 2013;Schüller et al., 2013); the archaic forms may also persist as coenophobic ruderals outside complexes of co-adapted species or as pioneer members of successions (Zherikhin, 1979;Dlusskiy, 1981;Kalandadze, Rautian, 1992;Kalandadze et al., 1995;Rautian, Zherikhin, 1997;Markov, Naymark, 1998).The actual distribution of taxa is customary reduced to two-dimensional contours on small-scale maps in biogeography (Makridin, Meyen, 1988), so that very different habitats, including the very specific ones are superposed as if they were one common habitat.Archaic forms populating these habitats in fact exist outside the area of ecological optimum for their higher taxon, i. e. outside the area of evolutionary advancing of this higher taxon.Such archaic forms are biologically in the same relations with the advanced relatives as the archaic forms that persist out of the diversification center of their higher taxon are with the advanced ones populating it.Timonin A. C. et al.Senecioneae (Asteraceae) of the Succulent Karoo and "geography of macroevolution of higher... be a result of the ordinary mechanism of the equatorial pump and does not unavoidably require zonal stratification of climates to be attributed to.

Concluding remarks
Specific traits of the flora of Senecioneae in the Succulent Karoo have allowed us to somewhat adjust the equatorial pump/out-of-the-tropics concepts.Fig. 8. Suggested corrected model of geography of macroevolution.Some taxon (Magenda) arises in region of taxon optimum and then spread into the pessimal/extreme area.More advanced representative of this taxon (Blue) evolves in the region of taxon optimum in time and replaces its original counterpart therein.However, it is unable to populate the pessimal/extreme area and remains in the region of optimum.Then, in the region of the optimum, another, even more advanced representative of the taxon (Violet) arises, which replaces its once-fortunate predecessor.It is able to adapt to the pessimal environment and spreads therefore into the pessimal/extreme area, where the original representative of the taxon still exists.This latest representative is too different from the original one for the two forms to compete with each other.Resultantly, the pessimal/extreme area is occupied by the primitive and most advanced representatives of the taxon.
The suggested version of these concepts is consistent with a wider range of biogeographic data.It makes possible to recognize a unified cause for a wider range of phenomena (Poleward latitudinal archaism gradient, reverse latitudinal archaism gradient, bi-directional archaism gradient, variously oriented archaism gradients).We think this version to be promising enough to spend time testing it with other research objects.