Cenostigma diversifolium (Benth.) Gaem, 2021

Gaem, Paulo Henrique, 2021, A nomenclatural note in Cenostigma (Leguminosae, Caesalpinioideae), Phytotaxa 498 (2), pp. 150-151 : 150

Cenostigma diversifolium (Benth.) Gaem , comb. et stat. nov.

Basionym:— Caesalpinia pyramidalis var. diversifolia Bentham (1870: 69) ≡ Poincianella pyramidalis var. diversifolia (Benth.) L.P. Queiroz (2010: 12) ≡ Cenostigma pyramidale var. diversifolium (Benth.) Gagnon & G.P.Lewis (2016: 71) . Type: BRAZIL. Maranhão: June 1841, Gardner 6006 (lectotype, designated by Lewis (1998); second-step lectotype, designated here: K000264577 [photo!]; isolectotypes: BM000952017 [photo!], K000264578 [photo!]).

A group of very similar taxa includes Cenostigma bracteosum ( Tulasne 1844: 141) Gagnon & G.P.Lewis in Gagon et al. (2016: 88), C. nordestinum Gagnon & G.P.Lewis in Gagon et al. (2016: 90), C. diversifolium comb . et stat. nov., and C. pyramidale ( Tulasne 1844: 139) Gagnon & G.P.Lewis in Gagon et al. (2016: 93), the two latter hitherto been considered varieties of the same species. These species are very similar in vegetative features and can be distinguished as pointed out in great detail by Lewis (1994, 1998) and Queiroz (2009): Cenostigma pyramidale s.s. is promptly recognised by the articulated pedicels below the middle of their lengths (vs. articulated directly below the ovary region in the other three taxa). Cenostigma bracteosum is characterised by its broadly ovate and showy bracts, and by larger lateral petals (15–17 mm long) (vs. not showy, ovate-lanceolate bracts and smaller lateral petals to 14 mm in the other three taxa). The two remaining species are distinguished from one another by the size of leaflets and bracts: those are greater in Cenostigma diversifolium than in C. nordestinum .

According to Lewis (1994, 1998), Cenostigma diversifolium and C. pyramidale s.s. (previously C. pyramidale var. diversifolium and C. pyramidale var. pyramidale , respectively) are distinguished from one another by terminal leaflet size, inflorescence indumentum colour, bract size, region of pedicel articulation, and standard claw apex, which sufficiently qualifies these taxa as independent species in the context where they are inserted and considering the current knowledge about this group, in my opinion. The same author also cites a resemblance between Cenostigma bracteosum and C. diversifolium , species that may frequently be misidentified without reproductive material.

In his book “ Caesalpinia : a revision of the Poincianella-Erythrostemon group”, Lewis (1998) designated the gathering Gardner 6006 at K as first-step lectotype of Caesalpinia pyramidalis var. diversifolia . At that time there was no barcoding system for Neotropical specimens in the Royal Botanic Gardens herbarium (G.P. Lewis, pers. comm.), and the two sheets of that collection were further considered two different specimens, receiving two different barcodes. Hence, I herein propose a narrowing second-step lectotypification according to Art. 9.17 of the International Code of Nomenclature for algae, fungi, and plants ( Turland et al. 2018).