A synopsis of Plagiocheilus (Compositae: Astereae)

A synopsis of Plagiocheilus (Compositae: Astereae) is provided, giving full synonymy, type citations and the location of known types, together with relevant notes and commentary, and the currently accepted distribution of each taxon; the distribution of taxa is also tabulated. Six species are recognised, one containing three subspecies. A key to species is presented. One author citation is corrected following an incorrect assumption by de Candolle when describing Plagiocheilus tanacetoides. The synonymy of Polygyne inconspicua, under Eclipta prostrata, is précised once again. An index to names associated with Plagiocheilus is given, and the nomen nudum of Plagiocheilus herzogii commented upon.


Introduction
During the recent extraction of material of Bolivian endemic Compositae, as part of a wider TIPAs (Tropical Important Plant Areas) Project at the Royal Botanic Gardens, Kew, material of Plagiocheilus Arn. ex DC. (Compositae: Astereae) provided a few problems, not least the historical determination of Ecuadorian material as P. ciliaris Wedd.which I consider a Bolivian endemic.
Plagiocheilus is a genus of six species ranging from Colombia in the north (P. bogotensis (Kunth) Wedd.) south to northern Argentina, Paraguay and Southern Brazil (P. tanacetoides Hook. & Arn. ex DC.) (see Table 1); the majority of species are Andean. First recognised by Arnott, and described by de Candolle (1838: 142), the genus was placed in the tribe Anthemideae (although considered a subtribe by de Candolle)the beginning of a tribal misplacement that has continued until relatively recently. Bentham (1873) maintained the tribal position, followed by Hoffmann (1892: 279), and in several Flora treatments, such as Baker (1884: 292 -293 -Brazil), Cabrera (1974: 421 -422 -Entre Rios, Argentina), Dillon (1981: 12 -15 -Peru), and Ariza Espinar (1997: 24 -Argentina). However, Robinson & Brettell (1973) quite convincingly argued that the genus was misplaced and belonged in the Astereae, a treatment followed by several authors, e.g. Nesom & Robinson (2006), Hind (2011 -Bolivia) and Sancho (2014: 231 -232 -Argentina). Its position in the Astereae was confirmed by Brouillet et al. (2009), where the two species sampled (P. bogotensis (Kunth) Wedd. and P. soliviformis DC.) were placed next to species sampled in Archibaccharis Heering. This supports the earlier proposals by Robinson & Brettell (1973), Grau (1977) and Bremer (1994). It is also clear from the molecular work that its position in the subtribe Grangeinae, as proposed by Nesom & Robinson (2006), is no longer tenable and that it is most probably best placed closer to, or in, the subtribe Hinterhuberinae s.str.
The species are perennial herbs and, with the exception of the more robust Plagiocheilus bogotensis and P. tanacetoides, dwarf species of high Andean grassland, all with bilabiate marginal floret corollas (with two inner lobes) which are whitish or reddish to purplish. The marginal florets are multiseriate, pistillate and female, and the achenes apically constricted, erostrate and epappose. Most of the Andean species are still rarely collected and all are poorly represented in herbaria, suggesting that further fieldwork and intensive collecting of all species might help further resolve the species delimitation presented below. Indeed, both Cuatrecasas (1954: 246 -247) and Dillon (1981: 15) have suggested that the variable and most widely distributed P. soliviformis DC. may well include within its variation P. ciliaris Wedd. and P. peduncularis (Kunth) Wedd.
In the following synopsis, a key to species is provided followed by a numerical listing of species. Distributions of the taxa are only provided at country level. No attempt has been made to determine the conservation status of any of the taxa because of the scarcity of collections and lack of field data on most labels, including collection altitude. It is hoped that someone will use it as the basis for a generic revision, especially to sort out the species relationships. A total of six species are recognised. Full synonymy, type citations and the location of known   (5521791), F(0051013), K(000634297dated 'Decemb r 1857'), P(00578720dated 'Decemb r 1857', 04396444dated 'Dec. 1865' on a small label, 04396445 and 04396447dated 'Decemb r 1857', 04396446dated 'Decemb r 1856' with variant locality data indicating 'in graminosis Cochipatal 3400-3800 m.'), RB (the label on this specimen was originally numbered '79', but this was crossed out and re-numbered as '83'). P(00578721) is also a duplicate of Mandon 79 ('Guaylla_aracha, au pied meme des rochers que sélvent jusquans neiges -H. 3300 m.'), but is annotated as Plagiocheilus ciliaris on the Mandon label, although this collection was listed by Schultz Bipontinus as 'Galinsoga parviflora Cav.' (Schultz Bipontinus 1865: 80); its collection date is stated as '7 8 bre 1858'! Clearly there is significant discrepancy amongst supposed duplicates of the same Mandon collection.
All were collected at about 300 m altitude in September 1911. The Oxalis and nolanas were all marked as 'n. sp.' in Herzog's account, although these were all published several years before. Plagiocheilus herzogii is not listed, even as a nomen nudum by either Koster (1945Koster ( , 1948 or Cabrera (1952) in their accounts of Herzog's Compositae collections (Chilean collections were cited even though the majority are Bolivian). Indeed, few appear to have been collected around Antofagasta. Marticorena & Quezada (1985) and Marticorena et al. (1998) did not list any taxon that might correspond to anything looking like Plagiocheilus with the exception of Cotula mexicana (DC.) Cabrera.
The position of Polygyne Phil. and Polygyne inconspicua Phil.

Acknowledgements
The author would like to thank two anonymous reviewers for some of their suggestions which have helped improve this paper.
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