Three new species of Pilea (Urticaceae) from limestone karst in China

Abstract Three hitherto undescribed species of Pilea (Urticaceae) from limestone karst in China are described and illustrated. Affinities of the species are discussed and Global Species Conservation Assessments presented. The new species are Pilea cavernicola A.K. Monro, C.J. Chen & Y.G. Wei, sp. nov. (Vulnerable) which most closely resembles Pilea scripta (Buch.-Ham. ex D.Don) Wedd. and Pilea gracilis Handel-Mazzetti, Pilea shizongensis A.K. Monro, C.J. Chen & Y.G. Wei, sp. nov. (Endangered) which is most similar to Pilea aquarum Dunn and Pilea guizhouensis A.K. Monro, C.J. Chen & Y.G. Wei, sp. nov. (Vulnerable) which resembles Pilea boniana Gagnep. and Pilea rubriflora C. Wright mostclosely.


Introduction
Pilea Lindley (1821: tab. 4) is the largest genus in the Urticaceae comprising ca 715 species (Monro, 2004) worldwide distributed throughout the tropics, subtropics and temperate regions (with the exception of Australia, New Zealand and Europe). Southeast Asia is the centre of morphological and phylogenetic diversity for Pilea whilst the Greater Antilles and Andean countries are the centres of species diversity (Monro, 2006). Pilea is easily distinguished from other Urticaceae by the combination of opposite leaves and a single, ligulate, intrapetiolar stipule in each leaf axil and pistillate fl owers with a 3-5 parted asymmetrical perigonium. Th e majority of species are succulent herbs, epiphytes or small shrubs growing in heavy shade at altitudes between 1000 and 3000 m above sea-level. Within China 81 species are recognised (Chen andMonro 2003, Chen andMonro 2007) and of these 32 are endemic.
As part of ongoing research into the diversity of cave-dwelling Urticaceae the authors undertook four fi eld trips to SW China in 2009 and 2010. Collecting was focused on the karst area in Guangxi, Guizhou and Yunnan and caves, stone forests (karst cockpit formations), gorges and natural forest were sampled. During the course of these collecting trips seven collections (not all in caves) corresponded to unknown species of Pilea, three of which are described here. Th eir affi nities are discussed and position within Weddell's (1869) and Chen's (1982) subdivision of the genus indicated, which although not phylogenetic, is based on the most comprehensive world-wide treatment of the genus.
Collecting in Karst is diffi cult as areas away from roads are sparsely populated and the terrain is steeply dissected and diffi cult to travel across. A consequence of this is that there are relatively few collections from such areas and undescribed species are frequently represented by very little material. Describing species based on a single or only two collections is problematic as there is no estimate of variation within the species and so the risk of over recognising species is greater. Th is is compounded in Floras such as China's where there has been a tradition of describing species from single collections resulting in a situation whereby the most closely related species may also be known from a single collection. Despite the above we have decided to describe one of the species in this manuscript based on a single collection as we feel that, given China's fast changing landscape and the fragility of many of the localities, to describe the species now aff ords the best hope for their conservation.

Methods
Herbarium specimens were compared with collections at IBK, BM and K and with scanned images of the collections at PE (http://pe.ibcas.ac.cn/herbinfor/vhtypequery. aspx) and HK (http://www.hkherbarium.net/Herbarium/tcc_pop.aspx) using the Flora of China. A morphological species concept developed during the course of previous taxonomic research on Pilea (Monro 2001 and2006) was employed to delimit and compare taxa. Material was examined under a Wild M3C binocular microscope and Planapo lens at X64 to X400 magnifi cations.
In the case of cave habitats, photosynthetically active radiation (PAR) was recorded. Observations of PAR were made at several points in the caves associated with living plants and expressed as micro moles per m2 per second (mmol/m2/sec) using a Skye instruments 180° panorama light meter for each point. Where available these observations are included in the Distribution section of the species descriptions.
Conservation assessments were undertaken using IUCN (2001) criteria B & D. Species distributions were plotted on Google Earth and the nature of the vegetation cover, urbanisation and road proximity surrounding sites, combined with observations in the fi eld, were used as indicators of plausible future threats. Diagnosis. Most similar to Pilea scripta from which it can be distinguished by the shorter stems, ovate rather than elliptic or oblong leaves, stipules with auriculate bases rather than deltate ones, the staminate tepals not ribbed and the sub-compressed elliptic rather than ovoid achenes with smooth non verrucose surfaces.
Distribution. North West Guangxi Province, ca 500-1000 m, caves in limestone karst, growing at any point from the back to the entrance of the cave, PAR 0.02-1.39 mmol/m2/sec (ca 0.04-2.78 % full daylight).
Etymology. Th e species name refers to the cave-dwelling habit of this species. Discussion. Comparison of the holotype and paratype material with type specimens from the herbaria listed in the methods section recovered Pilea scripta (Buch.-Ham. ex D.Don) Wedd. and P. gracilis Handel-Mazzetti as most similar to Pilea cavernicola. Pilea scripta can be distinguished from P. cavernicola based on stem height, leaf shape, stipule shape, staminate tepal morphology and achene morphology as summarised in Table 1. Pilea gracilis can be distinguished from P. cavernicola based on leaf shape, stipule morphology, staminate and pistillate infl orescence morphology and achene morphology as summarised in Table 2.  Chen's (1982) Urticella Section of the genus.

Pilea shizongensis
Distribution. Yunnan Province, Feng Huang Gu gorge, ca 1200 m, in limestone karst, growing on the fl oor of the gorge in deep shade.
Etymology. Th e species name refers to county of the locality of the only known collection of this species, Shizong.
Discussion. Comparison of the holotype material with type specimens from the herbaria listed in the methods section recovered Pilea aquarum Dunn as most similar to Pilea shizongensis. It can be distinguished from P. shizongensis based on pubescence, leaf margin morphology and pistillate tepal and fl ower morphology as summarised in Table 3.
Th ere is some confusion over the delimitation of Pilea aquarum and this is relevant to the delimitation of P. shizongensis. It would appear that the relatively rare character trait of pubescent pistillate tepals has been overlooked by several authors and that Pilea aquarum sensu strictu encompass a relatively narrow range of morphological variation which would exclude the subspecies P. aquarum subsp. brevicornuta and P. aquarum subsp. acutidentata.
Etymology. Th e species name refers to Province from which both collections of this species are known.
Discussion. Comparison of the holotype and paratype material with type specimens from the herbaria listed in the methods section recovered Pilea boniana Gagnep. and P. rubrifl ora C. Wright as most similar to Pilea guizhouensis. Pilea guizhouensis can be distinguished from Pilea boniana based on stipule, staminate, pistillate infl ores and achene length and staminate tepal number as summarised in Table 4. Pilea guizhouensis can be distinguished from P. rubrifl ora based on internode, stipule and, staminate and pistillate fl ower morphology as summarised in Table 5.
Conservation status. Using IUCN criteria (IUCN 2001) Pilea guizhouensis is considered Vulnerable (VU). Pilea guizhouensis is known from two localities (IUCN criteria D2, number of locations <5). Th ese two localities are ca 320 km apart and assuming that this species occurs within the 650-950 elevation range then the Extent of Occurrence between these localities is calculated to be 12,800 km2 (IUCN criteria B1, <20,000km2). Using the IUCN methodology our Global Conservation Assessment for P. guizhouensis is Vulnerable (VU) based on criteria B1 with a plausible future threat that could drive this taxon to Near Th reatened in a very short time. Plausible threats include the presence of a tourist trail running through the Malinghe Gorge which may be expanded, re-routed or rebuilt resulting in damage to the populations. In addition the second locality is located close to an agricultural area and is therefore vulnerable to conversion from forest to farmland.