Astereae, Cassini, 1819

Moraes, Pedro Luís Rodrigues De, 2020, Nomenclatural notes on the taxonomic identity of Sprengel’s Erigeron dubius, E. montevidensis, E. resinosus and E. filiformis (Asteraceae), Phytotaxa 438 (2), pp. 95-106 : 95-96

Tribe Astereae subtribe Conyzinae : circumscription of Erigeron , Hysterionica , and Neja

In a subtribal classification of the tribe Astereae Cassini (1819a: 195) , Nesom (1994c) has included in subtribe Conyzinae Horaninov (1847: 93) species of Apopyros Nesom (1994b: 177) , Conyza Lessing (1832: 203) , Erigeron , Hysterionica Willdenow (1807: 140) , Leptostelma Don (1831: 38) , and Neja D.Don in Sweet (1831: 78, tab. 78). Later, Nesom (2008) circumscribed Conyzinae including Erigeron , New World Conyza , the North American genus Aphanostephus Candolle (1836: 310) , and a small group of South American species segregated as the genera Apopyros , Darwiniothamnus Harling (1962: 108) , Hysterionica , Leptostelma , and Neja . As currently defined, the Conyzinae comprises about 500 species, about 400 of these generally identified as Erigeron ( Nesom & Robinson 2007, Nesom 2008), whose composition was essentially confirmed by a molecular-phylogenetic study of Erigeron and relatives ( Noyes 2000).

The genus Erigeron is one of the largest and taxonomically most difficult genera of the tribe Astereae ( Solbrig 1962) , being distributed in North to South America, West Indies, Galapagos, and Eurasia ( Nesom & Robinson 2007). Erigeron is usually characterized by its triangular-tipped stigmas with their surfaces covered by short and stubby collecting-hairs; by the possession of stout imbricated involucral bracts, arranged in approximately two series; and by its heterochromous heads, that is with the ligulate flowers of a different color from the tubular ones ( Solbrig 1962). However, according to Solbrig (1962), if these criteria were applied rigorously, many species hitherto referred to Erigeron would have to be excluded.

Among the segregates of Erigeron that are directly related to the species names treated in the present study, Hysterionica and Neja are of interest. Hysterionica was described by Willdenow (1807), based on H. jasionoides . It is a small genus endemic to south Brazil, Uruguay, Paraguay and Argentina. It is composed of annual or perennial herbs or sub-shrubs, taprooted; caudex simple; stems sometimes branched at base; leaves alternate, linear or lanceolate, glandular-pubescent; heads hemispheric, solitary; involucre formed by two or three series of linear bracts; receptacle flat or slightly convex, glabrous; flowers dimorphic: ray florets 1–3-seriate, pistillate, ligulate, yellow or white, usually with a very narrow ligule, limbs broad to filiform; disc florets hermaphrodite, yellow, with tubular corolla, lobes deltoid, erect; cypselae somewhat compressed, usually hairy; pappus 2-seriate: the outer series of very short linear scales and often somewhat flattened and chaffy; the inner series of long bristles, capillary; the inner capillary series is rarely missing; anthers rounded at base (adapted from Cabrera 1946 and Nesom & Robinson 2007).

Neja was described by D. Don in Sweet (1831), based on N. gracilis . It is a small genus of six species occurring in south-eastern South America and Cuba, according to the circumscription proposed by Nesom (1994a). It is characterized by perennial herbs, usually from taproot or branched caudex, with leaves mostly basal, filiform to linear-oblanceolate; heads solitary, long-pedunculate or on sparsely bracteolate stems; involucre broadly turbinate to hemispheric; bracts 2–4-seriate, gradate, narrowly triangular; rays pistillate, uniseriate, yellow or white; disc florets yellow, tubular, lobes deltate, erect; cypselae fusiform-cylindrical, with 7–10 prominulous orange-resinuous nerves, strigose between nerves; pappus bristles 1–3-seriate, outer series scarcely differing or of short setaceous bristles or scales ( Nesom & Robinson 2007).

The distinction between Hysterionica and Neja is tenuous, since they share characteristics such as the habit herbaceous, heads discoid, receptacles epaleate, white or yellow pistillate ray florets, yellow tubular disc florets, and pappus 2-seriate. As for the distinction, Hysterionica presents cypselae slightly compressed with 2–4-nerves and Neja has fusiform-cylindrical cypselae, with 7–10-nerves ( Nesom & Robinson 2007). Due to these morphological similarities, Neja has been considered as a synonym of Hysterionica by several authors (e.g., Bentham & Hooker 1873, Baker 1882, Cabrera 1946, Espinar 1980, Freire 2008). However, Nesom (1993) has recognized two groups of species within Hysterionica , the “ jasionoides group” (the typical element), and the “ pinifolia group”, based on differences in habit and leaf morphology, and in cypsela morphology (mainly the number of veins). From those differences, Nesom (1994a) segregated six species of Neja from Hysterionica , i.e. those belonging to the “ pinifolia group”: N. dianthifolia ( Grisebach 1879: 174) Nesom (1994a: 171) , N. filiformis ( Sprengel 1826: 520) Nees von Esenbeck (1839 : unpaged; 1840: 168), N. marginata ( Grisebach 1866: 149) Nesom (1994a: 171) , N. nidorelloides Candolle (1836: 325) , N. pinifolia ( Poiret 1808: 490) Nesom (1994a: 171) , and N. pulvinata ( Cabrera 1946: 353) Nesom (1994a: 172) . Nesom’s reinstatement of Neja has been accepted, for instance, by Nesom (2000, 2008), Nesom & Robinson (2007), Hind (2011), and Schneider et al. (2013), but not by Deble & Deble (2011) and Sancho & Vitali (2014), the latter treating Hysterionica in a broad sense, thus including Neja .

In the phylogenetic study of Erigeron and allies, based on the nuclear ribosomal internal transcribed spacer (ITS) region by Noyes (2000), accessions of 63 Erigeron species were included along with samples of nine species belonging to Aphanostephus , Apopyros and Conyza , further Hysterionica jasionoides and Neja filiformis . Noyes’s phylogeny and also the one reconstructed by Brouillet et al. (2009) have shown that Conyza , Neja , Hysterionica , Apopyros and Aphanostephus are deeply embedded within Erigeron , rendering Erigeron paraphyletic by these segregations, which are not supported by molecular data ( Brouillet et al. 2009). In other words, the subtribe Conyzinae essentially is equivalent to a monophyletic Erigeron . All other genera are derived from within the latter and could be considered synonyms ( Brouillet et al. 2009). These phylogenies have also indicated that Neja is probably the sister group to Hysterionica , notwithstanding the inclusion of only a single representative of each genus and the inference being based on only one molecular marker. Similar results from molecular markers have been found by Heiden (2014) through Bayesian inference trees. Trees based on nuclear subset analyses (ETS + ITS), on plastidial subset analyses (trn H- psb A + trn L-F), and on the combined analyses of both subsets, have shown that H. nidorelloides and N. filiformis formed a sister subclade to another subclade including samples of Apopyros warmingii ( Baker 1882: 23) Nesom (1994b: 179) , Conyza chilensis Sprengel (1818: 14) , and Leptostelma catharinense ( Cabrera 1957: 75) A.M.Teles & Sobral in Teles et al. (2008: 3). Until the achievement of a consensus on the circumscription of these genera, from phylogenies with representative sampling and a higher number of molecular markers, the currently accepted circumscriptions for Hysterionica and Neja are adopted here, proposing new synonymies related to the correct names.