Studies of systematic evolution and karyotypic variation in Smilax and Heterosmilax (Smilacaceae)

doi:10.1360/aps050125

Abstract

Abstract: Smilacaceae are a taxonomically confused, cosmopolitan family of Liliales characterized by their climbing habit, reticulate leaf venation, paired petiolar tendrils, unisexual flowers, and superior ovaries. Deviations from this generalized morphology have led the division of Smilacaceae into at least three different genera and five sections within the large genus Smilax. The karyotypes and chromosomes of 17 taxa of Smilax and Heterosmilax were examined and compared with previous studies of Smilacaceae. Phylogeny and karyotype evolution of the two genera are discussed in this paper along with evolutionary trends in inflorescence morphology, in the context of gene trees based on nrDNA ITS sequences. Karyotypes of these 17 taxa are characterized as follows: (1) “woody S. riparia”, 2n=32=L(2m+2st+2t)+M(4sm+4st)+S(2m+8sm+8st); (2) S. scobinicaulis, from Guizhou, 2n=32=L(2sm+4st+2t)+M(6sm(SAT)+2st)+S(2m+6sm+8st); (3) S. china in Shennongjia, Hubei is a diploid, 2n=32=L(6st)+M(4sm+6st)+S(2m+6sm+8st); (4) S. china in Guangxi with 4x, 2n=64=L(2sm+12st+2t)+M(4sm+8st)+S(6m+20sm+10st); (5) S. china from Japan with 4x chromosomes, 2n=64=L(4sm+14st+2t)+M(6st)+S(4m+28sm+6st); (6) S. trinervula from Guiyang, 2n=32=L(8st)+M(2sm+2st)+S(2m+6sm+12st); (7) S. chingii, 2n=32=L(2sm +6st)+M(4sm+4st)+S(2m+10sm+4st); (8) S. ferox from Kunming, a hexaploid, 2n=96= L(6sm+22st+6t)+M(2sm+10st)+S(6m+28sm+16st); (9) S. lebrunii from Sichuan, a hexaploid, 2n=96=L(4sm+24st)+M(4sm+10st)+S(10m+26sm+18st); (10) S. stans from Chongqing, 2n=32=L(4st+2t)+M(2sm+4st)+S(12sm+8st); (11) S. austro-zhejiangensis found in Zhejiang, 2n=32=L(4st+2t)+M(2sm+6st)+S(12sm+6st); (12) S. umbrosa found in Mt. Emei, 2n=32= L(2sm+6st)+M(2m+2sm+2st)+S(4m+8sm+6s); (13) S. bockii from Mt. Jingfo, 2n=32= L(2sm+6st)+M(6st+2m)+S(8sm+8st); (14) S. guiyangensis from Guiyang, 2n=32=L(6sm+ 2st)+M(4sm+2st)+S(2m+10sm+6st); (15) S. vanchingshanensis from Guizhou, 2n=32 =L(2sm+6st+2t)+M(4st)+S(4m+6sm+8st); (16) S. lunglingensis from Kunming, 2n=32= L(4st)+M(4sm+4st)+S(6m+6sm+6st); and (17) S. polycephala from Yunnan, 2n=32= L(2sm+ 6st)+M(2sm+6st)+S(6m+6sm+4st). The results showed that the karyotypes of Smilax and Heterosmilax are bimodal, with evidence of polyploidization, micro-variation, and variance of basic number from 16 to 15 and 13. We suggest that the karyotypes of the herbaceous Smilax species show a trend from symmetry in East Asian taxa to asymmetry in North America, but no such trend is obvious among woody species.

┌-L-┐ ┌-M-┐ ┌--S--┐

┌L┐ ┌-M-┐ ┌---S---┐

┌---L--┐ ┌----M---┐ ┌----S---┐

┌---L--┐ ┌-M-┐ ┌---S---┐

Regarding the inflorescence, we consider the prophyll to be a persistent bract. Therefore, the branches composed of single umbels borne in axils and with a prophyll at the base of the entire branch (i.e., sect. China and sect. Coilanthus) are homologous with the inflorescences possessing a prophyll at their base, or with a node on the peduncle and only a single umbel (in sect. Macranthae and sect. Smilax). Based on this interpretation and previous published ITS sequences, it is evident that a spike of umbels lacking peduncles is the primitive type of inflorescence in Smilacaceae from which two types of inflorescences are derived: (1) a solitary umbel without a prophyll, including species within Heterosmilax and Smilax section China and Coilanthus; and (2) a panicle-like type with one to many umbels subtended by a prophyll, i.e., the species of Smilax sect. Macranthae. Furthermore, our data suggest that Heterosmilax should not be recognized as a separate genus, but as a subgenus closely related to species of the herbaceous section of Smilax and Smilax sect. Coilanthus. The herbaceous species of Smilax, originating in East Asia and then expanding into North America, form a monophyletic group and a common ancestry with sect. Coilanthus. They are recognized as Smilax sect. Nemexia. Finally, studies of S. china show that it is a widespread species with varying ploidy levels. In this paper, a diploid population has been documented from Hubei, suggesting that tetraploid populations were widely distributed in East Asia when Japan and Taiwan separated from the Asian mainland during the Tertiary to Middle Pleistocene. Hexaploid populations, which are common on the mainland today, were probably generated by hybridization after their isolation. In conclusion, these results show that Southwest China is a center for the distribution and differentiation of Smilacaceae today.

Key words: karyotype, inflorescence, phylogeny, Smilax, Heterosmilax.

KONG Hang‐Hui, WANG Ai‐Li, LEE Joongku, FU Cheng‐Xin. Studies of systematic evolution and karyotypic variation in Smilax and Heterosmilax (Smilacaceae)[J]. J Syst Evol, 2007, 45(3): 257-273.

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Studies of systematic evolution and karyotypic variation in Smilax and Heterosmilax (Smilacaceae)

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