Journal of Systematics and Evolution 47 (5): 331–348 (2009) doi: 10.1111/j.1759-6831.2009.00054.x Evolution of the Madrean–Tethyan disjunctions and the North and South American amphitropical disjunctions in plants 1Jun WEN∗ 2Stefanie M. ICKERT-BOND 1(Department of Botany, MRC-166, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, USA) 2(UA Museum of the North Herbarium and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775-6960, USA) Abstract The present paper reviews advances in the study of two major intercontinental disjunct biogeographic patterns: (i) between Eurasian and western North American deserts with the Mediterranean climate (the Madrean– Tethyan disjunctions); and (ii) between the temperate regions of North and South America (the amphitropical disjunctions). Both disjunct patterns have multiple times of origin. The amphitropical disjunctions have largely resulted from long-distance dispersal, primarily from the Miocene to the Holocene, with available data indicating that most lineages dispersed from North to South America. Results of recent studies on the Mediterranean disjuncts between the deserts of Eurasia and western North America support the multiple modes of origin and are mostly consistent with hypotheses of long-distance dispersal and the North Atlantic migration. Axelrod’s Madrean–Tethyan hypothesis, which implies vicariance between the two regions in the early Tertiary, has been favored by a few studies. The Beringian migration corridor for semiarid taxa is also supported in some cases. Key words amphitropical disjunctions, biogeography, Madrean–Tethyan disjunctions, Mediterranean disjuncts, North–South American disjunctions. Intercontinental disjunctions have long interested organized these disjunctions according to continent biogeographers (e.g. Gray, 1846; Hooker, 1853; Raven, and latitudinal occurrence, and provided selected dis- 1963, 1972; Darlington, 1965; Thorne, 1972; Raven & tribution maps for each category. The 16 categories Axelrod, 1974; Wen, 1999, 2001; Manos & Donoghue, recognized by Thorne (1972) are: (i) Eurasian–North 2001; Donoghue & Smith, 2004; Sanmart´ın & Ronquist, American disjunctions; (ii) amphi-Pacific tropical dis- 2004; Xiang et al., 2004). Raven (1972) recognized sev- junctions; (iii) pantropical disjunctions; (iv) African– eral major patterns of intercontinental disjunctions as Eurasian (–Pacific) disjunctions; (v) Amphi–Indian follows: (i) in the north temperate zone among east- Ocean disjunctions; (vi) Asian-Pacific disjunctions; ern Asia, Europe/western Asia, eastern North Amer- (vii) Pacific Ocean disjunctions; (viii) Pacific–Indian– ica and western North America (the north temper- Atlantic Oceans disjunctions; (ix) American–African ate disjunctions); (ii) between Eurasian and western disjunctions; (x) North American–South American dis- North American deserts with the Mediterranean climate junctions; (xi) South American–Australasian disjunc- (the Madrean–Tethyan disjunctions); (iii) across south- tions; (xii) temperate South American–Asian disjunc- ern South America, Africa, and Australasia (southern tions; (xiii) circum-south temperate disjunctions; (xiv) Gondwanan disjunctions); (iv) between the Neotrop- circum-Antarctic disjunctions; (xv) subcosmopolitan ics and Africa (transatlantic tropical disjunctions); (v) disjunctions; and (xvi) anomalous disjunctions. Each of between the temperate regions of North and South these 16 major patterns of discontinuous biogeographic America (the amphitropical disjunctions); (vi) between distributions was further subdivided by Thorne (1972), temperate South America and Asia; and (vii) across with the third category (the temperate disjunction) hav- all major regions of the tropics (the pantropical dis- ing as many as 12 subcategories. junctions). Thorne (1972) undertook another review of With advances in molecular phylogenetics and new major disjunctions in plants and recognized 16 cate- tools for estimating divergence times, there is now re- gories with an additional 34 subcategories of biogeo- newed interest in studies of biogeographic disjunctions. graphically discontinuous distributions. Thorne (1972) Many analyses have been conducted on the classical temperate eastern Asian–eastern North American dis- junct pattern. This disjunct pattern has also been ex- amined in a broader framework of northern hemisphere Received: 7 August 2009 Accepted: 26 August 2009 ∗ biogeography (Wen, 1999, 2001; Manos & Donoghue, Author for correspondence. E-mail: [email protected]; Tel.: +1-202-633-4881; Fax: +1-202-786-2563. 2001; Donoghue & Smith, 2004). The tropical C 2009 Institute of Botany, Chinese Academy of Sciences 332 Journal of Systematics and Evolution Vol. 47 No. 5 2009 disjunctions in plants have been recently reviewed by stimulate additional work on these two patterns of Givnish and Renner (2004) and a few recent studies have disjunctions. explored the origin and evolution of the amphitropical disjunctions between North and South America (Vargas et al., 1998; Wen et al., 2002; Simpson et al., 2005; 1 Madrean–Tethyan disjunctions Moore et al., 2006). The Madrean–Tethyan disjunc- tion has been examined in several studies, including The Madrean–Tethyan disjunctions in plants were those of Fritsch (1996), Liston (1997), and Hohmann noted by Engler (1879), elaborated by Raven (1971, et al. (2006). Classical biogeographic models, such as 1973) and Thorne (1972), and reviewed by Liston Nothofagus Blume exhibiting a southern hemisphere (1997) from a molecular perspective. This disjunct pat- temperate disjunction and Liquidambar L. exhibiting an tern refers to the discontinuous distribution of con- intercontinental disjunction among eastern Asia, west- generic plants and sometimes conspecific taxa be- ern Asia/southern Europe, and eastern North America tween Mediterranean Eurasia and coastal western of the northern hemisphere, have also been re-examined North America. This pattern is sometimes known as with new analytical methods and new data sources (e.g. the Mediterranean–Californian disjunction (Hohmann Cook & Crisp, 2005; Ickert-Bond & Wen, 2006). et al., 2006) because many western North American el- Our understanding of northern hemisphere bio- ements showing this disjunction are largely distributed geography has progressed steadily in the past 15 years, in California. Five major regions have a Mediterranean- especially with regard to the phylogenetic relationships type climate characterized by hot, dry summers and of disjunct lineages and the timing of major biogeo- cool, moist winters. These regions include the Mediter- graphic patterns (Enghoff, 1995; Wen, 1999; Donoghue ranean basin in southern Europe and western Asia, west- et al., 2001; Sanmart´ın et al., 2001). Several disjunctions ern North America, central Chile, the Cape region of within the northern hemisphere have been better docu- South Africa, and southwestern and southern Australia mented and analyzed, such as the disjunctions between (Raven, 1971). Among these areas, the disjunctions be- eastern Asia–eastern North America (Wen,1999, 2001), tween Mediterranean Eurasia and California have been eastern Asia–western North America (Wu, 1983), the better documented, with approximately 35 plant genera trans-Atlantic disjunction (Manchester, 1999), and east- demonstrating such a disjunct pattern and some also ern North America–western North America (Wen et al., extending their distribution ranges to northern Africa 1996, 1998; Xiang et al. 1998). At present, the topic has (Thorne, 1972). Several are disjunct at the species level been actively investigated by systematists, ecologists, or at the level of species pairs (Stebbins & Day, 1967). and paleobotanists (Wen & Stuessy, 1993; Manchester, Three major hypotheses have been proposed to 1999; Wen, 1999, 2001; Donoghue et al., 2001; Li et al., explain the origin of the Mediterranean Eurasian 2001; Manos & Donoghue, 2001; Sanmart´ın et al., 2001; and western North American disjunction (Figs. 1, 2). Donoghue & Smith, 2004; Qian & Ricklefs, 2004; Xi- Axelrod (1973, 1975) proposed a nearly continuous ang et al., 2004; Yi et al., 2004; Li & Xiang, 2005; Nie trans-Atlantic belt of Madrean–Tethyan broadleaf ev- et al., 2005, 2006a, 2006b; Ickert-Bond & Wen, 2006). ergreen sclerophyllous vegetation stretching from west- These recent studies have demonstrated the complex ern North America to central Asia in the early Ter- history of migration, dispersal, and vicariance in the tiary (from the Eocene to the late Oligocene) at low northern hemisphere, as well as multiple origins of the latitudes (Fig. 1). The disjunct pattern in his view is classical disjunct pattern between eastern Asia and east- ancient and originated from floristic migration across ern North America, and suggested morphological stasis the North Atlantic. Conversely, others (Raven, 1972; among the disjunct lineages in the temperate zone (Wen, Raven & Axelrod, 1975) have argued for the origin 1999, 2001; Ickert-Bond & Wen, 2006). of this disjunct pattern via convergent evolution with The present paper reviews advances in studies of some disjunct taxa resulting from long-distance disper- two major disjunct patterns related to northern hemi- sal. Meusel (1969) also argued for the parallel evolution sphere biogeography, namely the Mediterranean dis- of disjunct taxa in Mediterranean-type climates in both junctions between the deserts of Eurasia and western western North America and western Eurasia. Stebbins North America (or the Madrean–Tethyan