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Penthorum humile

Description

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Family Saxifragaceae

Herbs or shrubs , rarely trees or vines . Leaves simple or compound , usually alternate or opposite, usually exstipulate . Flowers usually in cymes, panicles, or racemes , rarely solitary, usually bisexual , rarely unisexual , hypogynous or ± epigynous , rarely perigynous, usually biperianthial, rarely monochlamydeous , actinomorphic , rarely zygomorphic, 4- or 5(-10) -merous. Sepals sometimes petal-like. Petals usually free , sometimes absent. Stamens (4 or) 5-10 or many; filaments free; anthers 2-loculed; staminodes often present. Carpels 2, rarely 3-5(-10), usually ± connate ; ovary superior or semi-inferior to inferior, 2- or 3-5(-10) -loculed with axile placentation , or 1-loculed with parietal placentation , rarely with apical placentation; ovules usually many, 2- to many seriate , crassinucellate or tenuinucellate , sometimes with transitional forms; integument 1- or 2-seriate; styles free or ± connate. Fruit a capsule or berry, rarely a follicle or drupe. Seeds albuminous , rarely not so; albumen of cellular type, rarely of nuclear type; embryo small.

About 80 genera and 1200 species: worldwide; 29 genera (two endemic), and 545 species (354 endemic, seven introduced ) in China.

During the past several years, cladistic analyses of morphological, chemical, and DNA data have made it clear that the recognition of the Saxifragaceae sensu lato (Engler, Nat. Pflanzenfam. 18a: 74-226. 1928) is untenable. Among the angiosperm families, Saxifragaceae sensu lato may in fact represent the most extreme example of a polyphyletic assemblage . For example, recent analyses of DNA sequence data indicate that these taxa represent at least ten separate evolutionary lines , many of which are only distantly related to one another (Morgan & Soltis, Ann. Missouri Bot. Gard. 80: 631-660. 1993; Soltis & Soltis, Amer. J. Bot. 84: 504-522. 1997) . Furthermore, very large molecular phylogenetic analyses of hundreds of angiosperms indicate that these separate lineages are distributed among four of the six traditionally recognized subclasses of dicotyledons (Savolainen et al. , Syst. Biol. 49: 306-362. 2000; Soltis et al., Nature 402: 402-404. 1999) . These recent studies have also greatly clarified how this phylogenetically diverse assemblage should be divided into families and treated taxonomically (see The Angiosperm Phylogeny Group (APG), Ann. Missouri Bot. Gard. 85: 531-553. 1998) . Recent studies of DNA sequence data have clarified both the circumscription and affinities of a narrowly defined Saxifragaceae (Saxifragaceae sensu stricto) and Hydrangeaceae (Soltis et al., Amer. J. Bot. 82: 504-514. 1995; Savolainen et al., loc. cit. ; Soltis et al., loc. cit. 1999) . Saxifragaceae sensu stricto should consist only of Saxifragoideae, a group of about 30 herbaceous genera. Members of Saxifragaceae sensu stricto from the Chinese flora include Astilbe, Astilboides, Bergenia, Chrysosplenium, Mitella, Mukdenia, Oresitrophe, Rodgersia, Saxifraga, Tanakaea, Tiarella, and the recently described Saniculiphyllum. Close relatives of Saxifragaceae sensu stricto include Itea, Penthorum, and Ribes. These genera, the sole members of Iteoideae, Penthoroideae, and Ribesioideae, respectively, are also best treated in separate families: Iteaceae, Penthoraceae, and Grossulariaceae (see APG, loc. cit.) . These taxa, as well as several others, such as Crassulaceae, are basal to a large assemblage of taxa, most of which were traditionally placed in Rosidae . Sequence data also indicate that Parnassia (the sole member of the Parnassioideae) is a more derived member of the rosid alliance , most closely related to Brexia and Lepuropetalon (also part of Saxifragaceae sensu lato) and Celastraceae. Parnassia and Lepuropetalon should be placed in Parnassiaceae with Brexia part of an expanded Celastraceae (APG, loc. cit.) .

Both morphological and molecular data indicate that Hydrangeoideae and Escallonioideae are, in contrast, allied with taxa traditionally placed in Asteridae. Hydrangeoideae are a well-defined, monophyletic lineage that should be treated as Hydrangeaceae. In China they include Cardiandra, Decumaria, Deinanthe, Deutzia, Dichroa, Hydrangea, Kirengeshoma, Philadelphus, Pileostegia, Platycrater, and Schizophragma, and are closely allied with families such as Cornaceae, Loasaceae, and Nyssaceae. Escallonioideae appear to be polyphyletic, and this group of approximately 14 genera is in need of thorough study. Members of this subfamily are allied with several different lineages of higher asterids. Polyosma, the only member of Escallonioideae in China, appears closely allied with Caprifoliaceae (Xiang & Soltis in Boufford & Ohba, Sino-Japanese Flora: its Characteristics and Diversification, 1998) .[1]

Genus Penthorum

Herbs perennial , erect , fibrous rooted. Stems terete , glabrous proximally to finely pubescent and widely branched distally. Leaves alternate, shortly petiolate ; leaf blade lanceolate or narrowly so, thin, apex long acuminate. Flowers numerous , arranged in terminal and axillary , scorpioid (or corymblike) cymes, bisexual , yellow-green, small. Sepals 5(-8). Petals 5(-8) or absent. Stamens 10(-16), in 2 whorls. Carpels 5(-8), connate near base ; ovules many; styles short. Capsule 5(-8) -lobed; carpels rostrate at apex. Seeds many, small.

Two morphologically very similar species: one in E Asia, the other in E North America; one species in China.

Recent studies have demonstrated that Penthorum is not part of Saxifragaceae, but is actually most closely related to Haloragaceae.[2]

Taxonomy

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Notes

Publishing author : Regel & Maack Publication : in Regel, Tent. Fl. Ussur. 65.

Similar Species

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Members of the genus Penthorum

ZipcodeZoo has pages for 2 species, subspecies, varieties, forms, and cultivars in this genus:

P. chinense (Penthorum) · P. sedoides (Ditch Stonecrop)

More Info

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Further Reading

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Notes

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Contributors

Identifiers

Footnotes

  1. Jin-tang Pan, Cuizhi Gu, Shumei Huang, Chao-fen Wei, Shu-ying Jin, Lingdi Lu, Shinobu Akiyama, Crinan Alexander, Bruce Bartholomew, James Cullen, Richard J. Gornall, Ulla-Maj Hultgård, Hideaki Ohba & Douglas E. Soltis "Saxifragaceae". in Flora of China Vol. 8 Page 269. Published by Science Press (Beijing) and Missouri Botanical Garden Press. Online at EFloras.org. [back]
  2. Pan Jintang, Douglas E. Soltis "Penthorum". in Flora of China Vol. 8 Page 271. Published by Science Press (Beijing) and Missouri Botanical Garden Press. Online at EFloras.org. [back]
Last Revised: 2014-05-10