Dysaster cajamarcensis, a new shrubby genus and species of Astereae (Asteraceae) from Peru

Abstract Dysaster cajamarcensis is a spreading broad-leaved shrub named as a new genus and species of the tribe Astereae subtribe Hinterhuberinae collected in northern Peru. It has bisexual disc florets, disc style branches with strong stigmatic lines and hairy appendages, compressed achenes in both ray and disc florets, and papyraceous involucral bracts.


Introduction
Th ere is something very unsatisfying about a plant, sent for identifi cation, that has no strikingly distinctive feature, but has a combination of characteristics that excludes it from any already known genus. It is particularly unsatisfying when the plant involved is a member of a tribe such as the Astereae in which phyletic studies using DNA (Brouillet et al. 2009) are not yet adequately correlated with morphological and anatomical studies. Nevertheless, such a plant has been collected in northern Peru. Th e specimen of the broad-leaved shrubby plant arrived with a fi eld identifi cation of Diplostephium , the latter a genus of shrubby Astereae that is common in the Central and Northern Andes. Th e plant is not a Diplostephium Kunth, and has characteristics that do not agree with any other genus in the tribe.
Attempts to identify the plant have involved the use of keys in Hoff mann (1890-1894), Cuatrecasas (1969), Nesom and Robinson (2007), Strother and Brouillet (2006), and lists of genera and species in Braco and Zarucchi (1993), and the genera sequenced in the treatment by Brouillet et al. (2009). Results were as follows.
Th e treatment by Brouillet et al. (2009) includes no unaccounted for elements among the listed South American Astereae. More importantly, all of the Astereae listed in the Catalogue of the Flowering Plants and Gymnosperms of Peru (Brako and Zarucchi 1993) and in the treatment of the tribe in Colombia (Cuatrecasas 1969) can be excluded. Th e keys to genera in various treatments are not much more helpful. In Hoff mann (1890-1894) the plant keys into the relationship of Sommerfeltia Less., but the latter is a distinctive element from southeastern South America with deeply dissected leaves. In Cuatrecasas (1969) the new entity keys to Aster L., a concept that in that work was based on two introduced species now known to be Symphyotrichum Nees. Th e Peruvian plant also keys to the Symphyotrichum relationship in Nesom and Robinson (2007), but the involucral bracts are totally non-herbaceous. When keyed among North American genera in Strother and Brouillet (2006), the Peruvian plant comes to Ampelaster G.L. Nesom, another member of the Symphyotrichum relationship.
One further possibility exists. Th e involucral bracts have a median dark stripe that might be indicative of the resin duct characteristic of the subtribe Conyzinae. Among the genera of that subtribe, the new entity would key in Nesom and Robinson (2007) to Darwinothamnus Harling. Th e latter is endemic to the Galapagos Islands, and it is a linear-leaved rather ericoid-looking plant with infl orescences not or scarcely exserted. It has chaffi er, more recurved involucral bracts and small narrow limbs on the ray fl orets. Th e achenes in Darwinothamnus are sparsely setuliferous on the faces rather than densely spiculiferous, and the marginal ribs contain enlarged resin ducts. Th e pappus lacks a well-defi ned outer series, and bristles have tenuous rather than broadened tips.
A comparison on a broad scale using preliminary DNA sequencing (ITS1 & 2) places the new entity among previously sequenced Astereae that are almost all members of the subtribe Hinterhuberinae. Th e genera that show closest correlation are Hinterhubera Sch. Bip. ex Wedd., Parastrephia Nutt., Guynesomia Bonifacino & Sancho, the diminutive epappose Laestadia Kunth ex Less., and Diplostephium . Of these, Hinterhubera is an ericoid, mostly narrow-leaved genus of Colombia and Venezuela that has narrow corolla lobes and functionally male disc fl orets. Parastrephia is a genus of cupressiform resinous shrubs with bisexual disc fl orets and nearly terete achenes from mostly southern Peru, Bolivia and Chile. Guynesomia is a plant with sparse linear leaves, bisexual fl orets and scarcely compressed achenes that is endemic to Chile. Th ere remains Diplostephium which is the only genus in the group that has species that are remotely similar in habit to the unknown entity from northern Peru. None of these show DNA correlation closer than 97%.
In spite of all the results from various keys and DNA results, it is the genus Diplostephium in which the Peruvian plant was placed by the collectors, and it is that genus with which it is most likely to be confused on brief observation. Th e new genus and Diplostephium diff er in fi ve signifi cant characteristics.
(1) Th e achenes of the new entity are compressed with only two ribs in both ray and disc fl orets; (2) Th e disc fl orets are fully bisexual with style branches having well-developed stigmatic lines; (3) Involucral bracts are narrowly lanceolate and sharply pointed with a dark median stripe outside; (4) the outer pappus is a strongly diff erentiated series of squamae; and (5) the infl orescence is exserted well beyond the foliate parts of the branches and has few heads on long peduncles.
Diplostephium has more triangular and prismatic achenes, functionally male disc fl orets lacking stigmatic lines on their style branches, involucral bracts that are more ovate, less pointed, and without an external median stripe, a less strongly diff erentiated outer pappus series that has shortened bristles of variable lengths, and an infl orescence that is usually dense and mostly sessile, rarely subumbellate.