There is something very unsatisfying about a plant, sent for identification, 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. The specimen of the broad-leaved shrubby plant arrived with a field identification of Diplostephium, the latter a genus of shrubby Astereae that is common in the Central and Northern Andes. The 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 Hoffmann (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.

The 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. The keys to genera in various treatments are not much more helpful. In Hoffmann (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. The 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. The 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. The latter is endemic to the Galapagos Islands, and it is a linear-leaved rather ericoid-looking plant with inflorescences not or scarcely exserted. It has chaffier, more recurved involucral bracts and small narrow limbs on the ray florets. The achenes in Darwinothamnus are sparsely setuliferous on the faces rather than densely spiculiferous, and the marginal ribs contain enlarged resin ducts. The pappus lacks a well-defined 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. The 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 florets. Parastrephia is a genus of cupressiform resinous shrubs with bisexual disc florets and nearly terete achenes from mostly southern Peru, Bolivia and Chile. Guynesomia is a plant with sparse linear leaves, bisexual florets and scarcely compressed achenes that is endemic to Chile. There 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. The new genus and Diplostephium differ in five significant characteristics.

(1) The achenes of the new entity are compressed with only two ribs in both ray and disc florets;

(2) The disc florets 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 differentiated series of squamae; and

(5) the inflorescence 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 florets lacking stigmatic lines on their style branches, involucral bracts that are more ovate, less pointed, and without an external median stripe, a less strongly differentiated outer pappus series that has shortened bristles of variable lengths, and an inflorescence that is usually dense and mostly sessile, rarely subumbellate.

The Peruvian entity is named here as new at both the generic and species level.