Synopsis of Plazia Ruiz & Pav. (Onoserideae, Asteraceae), including a new species from northern Peru

Abstract A synopsis of Plazia Ruiz & Pav. (Onoserideae, Asteraceae) is presented, including the description of a new species, Plazia robinsonii M.O.Dillon & Sagást., from a locality c. 20 kms west of Huamachuco, Department of La Libertad in northern Peru. It most closely resembles Plazia conferta Ruiz & Pav., a narrow endemic from central Peru some 450 km to the south; however, the latter species has larger leaves and smaller capitula. Plazia is a small genus of four species confined to the Andean Cordillera of Peru, Bolivia, Chile, and Argentina. A distribution map of the four species, an illustration of the new species, a photograph of the holotype, and a key to species are provided.


Introduction
Plazia Ruiz & Pav. (Mutisioideae, Asteraceae) is a distinctive genus confi ned to the Andean Cordillera of Peru, Bolivia, Chile, and Argentina. It is easily recognized by its suff rutescent and decidedly woody habit with stems to a meter or more. Th e sessile leaves are tightly clustered and confi ned to the terminal 10-20 cm portions of the branch apices, the radiate capitula have ray fl orets with whitish to pink corollas and dark purple anthers long-exerted from the disc whitish fl orets.
Phylogenetic studies have shown that the genus Plazia belongs to the tribe Onoserideae, along with the genera Aphyllocladus Wedd., Gypothamnium Phil., Lycoseris Cass . , Onoseris Willd., and Urmenetea Phil. (Panero and Funk 2008, Katinas et al. 2008, Luebert et al. 2009, Panero 2009). Th ese studies also show that the genus Plazia forms a clade within the Onoserideae together with Aphyllocladus and Gypothamnium . Recently, Panero and Freire (2013) suggested the inclusion of the genus Paquirea Panero and S.E. Freire in the tribe Onoserideae, associating it with Plazia , but provided no phylogenetic evidence to support that.
Distribution. All species are confi ned to the Andean Cordillera and associated inter-Andean valleys (Fig. 1). Two species are confi nded to Peru; both are rare and only known from a few collection localities. Another species is restricted to the Andes of central Chile. Plazia daphanoides Wedd. is the only wideranging species, being recorded from southern Peru and adjacent Argentina, Bolivia and Chile, usually in highelevation, dry sites (Cabrera 1978, Ferreyra 1980, 1995. Discussion. Th e genus Plazia was described by Ruiz López and Pavón (1794) and they subsequently published its fi rst species, P. conferta Ruiz & Pav. (1798). All eff orts at locating material corresponding to their type collection from Peru have not been successful (Cabrera 1960). Weddell (1855) provided an emended generic description for Plazia and he recognized three species: Plazia conferta Ruiz & Pav., P. cheiranthifolia (J. Remy) Wedd., and P. daphnoides Wedd. Reiche (1905) Cabrera 1978, Ferreyra 1995, Hind 2009, Marticorena and Quezada 1985, Zuloaga and Morrone 1999. Th e addition of the northern Peruvian species described here brings the total number of recognized species to four. Leaves oblong or oblong-spathulate, 8-18 mm long, 2-3.5 mm wide; capitula with 5-8(-10) ray fl orets, (7-)10-11(-12) disc fl orets; involucres cylindrical (Argentina, Bolivia, Chile, Peru Distribution. While it was once considered extinct, this species was recently rediscovered in the Precordillera of Ovalle (Faúndez and Saldivia 2008) and the description provided here is largely derived from the specimens and data in that publication. Since this species appears to be restricted to an area of no more than 2 km 2 , it would be designated as "critically endangered" (IUCN 2001).

Key to species of Plazia
Discussion. Plazia cheiranthifolia is a rare shruby species apparently confi ned to the central Chilean region near Coquimbo. It has the longest leaves of any species of Plazia and large capitula with broadly campanulate involucres. Rémy described as his Aglaodendron chieranthifolium as homogamous, all with bilabiate corollas with lobes of varying lengths. From the photo in Faúndez and Saldivia (2008), it appears there are perhaps nine subligulate corollas.
Discussion. Plazia conferta is a rare species, and type material has not been located. No new material had been collected since Ruiz López and Pavón's original gathering until a second collection was made by Felix Woytkowski at the type locality nearly 180 years after its original description. Cabrera (1960) was unsuccessful in locating Ruiz López and Pavón's type material in the major European herbaria, including Madrid. We made inquiries to the Real Jardín Botánico in Madrid, but no collection of Plazia has surfaced as yet. Ferreyra (1980) cited duplicates of Woytkowski 52 as occurring at MO and F, but after exhaustive searching, no duplicate collections were located, and subsequently the duplicates were not cited in Ferreyra's Flora of Peru treatment (1995). Further, during this study, we were unsuccessful in our eff orts to examine the Woytkowski collection at USM, and the description provided by Ferreyra (1995) was used to quantify the diff erences between that species and the new one described here.

Plazia daphnoides
Discussion. Th is species is distinctive with the narrowest capitula with the fewest ray and disc fl orets within the genus. Ferreyra (1995) lists the type specimen as collected by H. Weddell near the locality of Tacora, which is now in northern Chile.
Weddell (1855) failed to describe a nominative variety (p. 13); however, the manner in which he presented the material examined in his studies suggests that his fi rst variety represented his nominative variety [α villosa, foliis utrinque villosis]. Examination of a large suite of collections has failed to fi nd consistant morphological variation combined with any geographic pattern to support recognition of varieties in this taxon. Robinson's (1980) new genus and species, Harthamnus boliviensis , was discovered by him to be a synonym of Plazia daphnoides shortly after its publication.
Discussion. Th e duplicates of the type collection of this new species were originally distributed under the generic name Diplostephium Kunth (1818), a member of the tribe Astereae. Th e overall morphology of the material does superfi cially resemble some members of Diplostephium , however, the bilabiate corollas, truncate style branches, and anther tails are typical for the Mutisieae not the Astereae. Th e new species was uncovered after the Flora of Peru treatment (Ferreyra 1995) was published and set aside for investigation. Only recently was the material encountered during routine fi ling, having been misplaced for nearly two decades.
Th e type locality is approximately 450 km north of its nearest congener, Plazia conferta, from near Tarma. Although the region where the original collections were made has been visited by numerous botanists, to our knowledge this species has not been recollected since 1974 when it was encountered by Abundio Sagástegui Alva and  Arnaldo López Miranda. Casual eff orts to fi nd the plant again have not met with success. Given that the plant is quite showy and distinctive, it should not go undetected for long if it is indeed extant.
Etymology. Th is species honors Dr Harold Robinson, Senior Research Curator at the National Herbarium, Smithsonian Institution. He suggested with his annotation of the US sheet, designated as an isotype, that this taxon was perhaps a new species of Plazia , and not an unusual Diplostephium , as had been suggested on the original label.