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Phylogenetic Placement of the Enigmatic and Critically Endangered Genus Saniculiphyllum (Saxifragaceae)
source:Key Laboratory of Biodiversity and Biogeography, CAS     author:XIANG Chunlei     2012-07-03

The monotypic Saniculiphyllum, comprising the single species S. guangxiense C.Y. Wu & T.C. Ku, is a clonal aquatic herb clinging to the wet rocks or stone in brooks in southeast Yunnan Province and Northwest of the Guangxi Zhuang Autonomous Region. The species is considered to be endangered and was actually thought to be extinct before the recent rediscovery of several populations in Yunnan. The populations in Tianlin County of Guangxi Zhuang Autonomous Region of southern China, from where the type specimens of the species were collected in 1989, had disappeared due to seasonal drying of the streams and plants never been found in this area again.

The systematic position of Saniculiphyllum has been enigmatic ever since its publication. When establishing the genus, WU and KU (1992) placed it within its own tribe, Saniculiphylleae within Saxifragaceae. Mabberley (1997) elevated the genus to the rank of family, but as Saniculophyllum and Saniculophyllaceae. Based on its thick rhizomes and palmately lobed leaves, Soltis (2007) thought that this genus might belong to the Darmera group in Saxifragaceae. However, at the same time, he also stressed that it was more appropriate at that point to consider the exact placement of the genus within Saxifragaceae as unknown.

Here PENG Hua’s research group from Kunming Institute of Botany analyzed six DNA regions, the nuclear ribosomal ITS and 26S rDNA and the plastid rbcL, matK, trnL-trnF, psbA-trnH genes, spacers, and intron to explore the phylogenetic position of Saniculiphyllum within Saxifragaceae. The combined nuclear and chloroplast dataset includes 63 ingroup species, representing all genera but Hieronymusia in the family. Results from likelihood, parsimony and Bayesian phylogenetic methods corroborate earlier results. Two clades of Saxifragaceae, the Heucheroid and Saxifragoid clades, were recovered. The topologies obtained from different analyses confirm the placement of Saniculiphyllum in Saxifragaceae, but our analyses reveal that Saniculiphyllum is embedded within the large Heucheroid clade. However, the closest relatives of Saniculiphyllum within the Heucheroid clade remain unclear. Combined with morphological data, our results suggest that Saniculiphyllum should best be regarded as a highly distinctive lineage within the Heucheroid clade of Saxifragaceae.

In this present study, the phylogenetic inferences imply that several morphological character states, especially carpel number that were held as unique and characteristic of Saniculiphyllum, actually evolved independently. Most species of Saxifragaceae standardly have 2 carpels, as do closely related genera (e.g., Itea, Ribes). Five genera, Astilbe of Astilbe group, Conimitella, Micranthes, Bergenia and Rodgersia of Heuchera group occasionally have 3 carpels. Only the genus Lithophragma of the Heuchera group, is characterized by 3 carpels. However, based on our investigation of 491 flowers, Saniculiphyllum has three different carpel numbers. The percentages of 3, 4 and 5 carpels are 28.72%, 45.62% and 25.66% respectively, of which 4 and 5 carpels are unique to Saniculiphyllum within Saxifragaceae (Fig. 2), while 2 carpels, which was reported in the original description (WU and KU, 1992), could not be found in our samples.

This work is published by Molecular Phylogenetics and Evolution (2012. 64: 357-367.) and supported by the National Natural Science Foundation of China (No. 30770152) granted to LGL and partially financed by the Angiosperm Tree of Life Project (NSF EF-0431266) to DES. (http://www.sciencedirect.com/science/article/pii/S1055790312001492)

Fig.1  Photographs of Saniculiphyllum guangxiense in its natural habitat. (a and b) habitat of S. guangxiense in Funing County. (a) Group of individuals growing on cliff near water; (b) the plants of S. guangxiense cling to stones in stream; (c) details of S. guangxiense showing the leaves palmately deeply lobed; (d and e) floral form of the species; (d) cymes with 7–10 flowers; (e) flower, showing five red petals, five stamens, and three carpels; (f, g, and i) rhizomes and fibrous roots; (f) long and horizontal rhizomes cling to stone; (g) densely fibrous roots; (i) details of fibrous roots under stereo microscope; (h) ovules; (j) details of seeds showing that these seeds generally hypogenetic. (Image by KIB)

Fig. 2  Three types of carpels of S. guangxiense. (a) Three carpels; (b) four carpels; (c) five carpels. (Image by KIB)


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