Chromolaena medullosa (Urb.) B.Ferlay, 2025

Ferlay, Benjamin, 2025, Neotypification and new combination for an endemic species of Martinique (Lesser Antilles) in the genus Chromolaena (Eupatorieae, Asteraceae), Phytotaxa 698 (1), pp. 51-57 : 52-54

Chromolaena medullosa (Urb.) B.Ferlay , comb. nov.

Basionym:— Eupatorium medullosum Urban (1903: 393) .

Type: — MARTINIQUE. Duss 295b, 295c (holotype B †). MARTINIQUE. Piton Dumauzé, tropical humid montane scrubland, 14°41’35.5488’’N, 61°6’4.158’’W, 909 m, 16 June 2024, B. Ferlay 3100 (neotype MTK 006994!, designated here) ( Figs. 1 & 2 ).

Description:— Shrub 0.6–1 m tall. Stems thick, terete, slightly striate, medullary, pubescent, multicellular whitish hairs, becoming glabrescent with age, bearing sessile resinous glands. Leaves opposite, oval to narrowly oval, more or less rugose, chartaceous-coriaceous to coriaceous, 3.5–5 cm long × 2–3.5 cm wide, with a rounded to broadly and shortly cuneate, obtuse base, obtuse to rounded apex, crenate to dentate margins except at the base. Blade with numerous cavities containing sessile resinous glands on the abaxial surface, more scattered on the adaxial surface, hairs mostly along veins and veinlets on the abaxial surface, rarer on the adaxial surface, all multicellular. Petioles thick, 2–3 mm in diameter, 2–4 mm long, densely pubescent with multicellular hairs. Pinnate venation, with two closely spaced basal pairs of veins, veins prominent on abaxial surface, impressed on adaxial surface. Terminal inflorescences in a compact corymb, more or less globose, 2–3 cm long × 3–7 cm wide. Capitula on pedicels 0–9 mm long, more or less pubescent with multicellular hairs, 7–8(–9) mm long × 3–4 cm wide, with approximately 25 florets. Capitulum scales densely imbricate, about 45 in number, arranged in 6–7 series; outer scales semi-ovate, 1–1.5 mm long; intermediate scales orbicular to oval, 1.5–2 mm long; innermost (internal) scales elliptical to oblong-linear, 4–5 mm long × 0.8–1.5 mm wide, all with obtuse to rounded apices, ciliate to fimbriate margins, sometimes bearing a few resinous glands on the upper part. Achenes 2.1–3.0(–3.5) mm long, excluding the pappus, with 3–4 sabre-shaped cartilaginous ribs, bearing 25–45 uniseriate pappus at the apex arranged in a disk, 2.4–2.9 mm long.

Phenology: —This species flowers from the middle to the end of the dry season, e.g. March to June (Ferlay 1264, 3100; pers. obs.). The fruiting period overlaps with the flowering period.

Additional specimens examined: — MARTINIQUE. Pitons du Carbet, February 1865, Hahn 797 ( P02410730 ) ; Pitons du Carbet, 25 August 1936, Privault 278 ( P02410734 ) ; Morne Piquet , 23 April 1994, Sastre & Le Hir 9327 ( P02839561 ) ; Morne Macouba , 24 January 2007, Sastre & Nicolas 10170 ( P04453696 ) ; Montagne Pelée , 01 March 2020, B. Ferlay 414 ( MTK002975 ) ; Piton de l’Alma , 29 May 2021, B. Ferlay 1264 ( MTK003946 , P00942003 ) .

Distribution and habitats: — Chromolaena medullosa is endemic to Martinique, occurring in the mountainous areas at elevations above 900 m, primarily in the montane scrublands of Pitons du Carbet, and is more localized at Montagne Pelée ( Fig. 3 ). It is found with the low herbaceous or semi-woody species as Parablechnum ryanii (Kaulf.) Gasper & Salino in Gasper et al. (2016: 217, Blechnaceae ), Besleria lanceolata Urban (1901: 351 , Gesneriaceae ), Ischaemum latifolium (Spreng.) Kunth (1829: 168 , Poaceae ), Machaerina restioides (Sw.) Vahl (1805: 238 , Cyperaceae ) or Chaetogastra chamaecistus Sieber ex Grisebach (1860: 267 , Melastomataceae ).

Conservation status: —Using the GeoCAT application, the species is classified as CR according to EOO and EN according to AOO. Chromolaena medullosa occurs in a limited number of localities, fewer than 10, with one locality being highly isolated from the others (Montagne Pelée). However, the number of individuals does not appear to be declining and is estimated between 250 and 2,500 mature individuals. Moreover, its habitat is not threatened, neither by destruction nor by alien species (all individuals are located within a protected area). Depending on the locality, slight fluctuations in individual abundance can be observed, potentially explained by its presence on steep slopes, which are prone to landslides. Its low representation on Montagne Pelée may be due to past volcanic eruptions of this massif, which likely impacted the populations. The species might be threatened by climate change in the future, but currently, there is no evidence of global changes impacting montane species in the Lesser Antilles. Considering the stated information, C. medullosa can be classified as EN B2ac(iii).

Note: —Specimen from the mountainous massifs of Martinique have been identified as Eupatorium medullosum (Belanger 521 [P02410728, P02410735], Hahn 170 [P02410726, P02410729, P02410737], Joseph Ewan 17091 [NO0012293], Plée 773 [P02410727], Sastre 6560 [P02839560], Sastre 6852 [P0239552], Sastre 9761 [P02839558], Stehlé 1004 [P02410731], Stehlé 1014 [P02410724], Stehlé 2394 [P02410733], Stehlé 8187 [P02410732]), are actually Chromolaena trigonocarpa . Although C. trigonocarpa is more localized in montane thickets, it can sometimes be found at lower elevations in montane scrublands (alongside C. medullosa ). In the latter, individuals are often more stunted, with smaller leaves and smaller inflorescences than those found in more shaded habitats. Nevertheless, leaf shape remains constant (acute apex), allowing it to be easily distinguished from C. medullosa (broadly obtuse to rounded apex).

Figures

FIGURE 1. Image of the neotype of Chromolaena medullosa, B. Ferlay 3100 (MTK006994).

FIGURE 2. Chromolaena medullosa (A–D. from the fresh specimen of the neotype; B. Ferlay 3100). A. Plant in its habitat; B. Detail of an inflorescence; C. Adaxial surface of a leaf; D. Abaxial surface of a leaf; E. Habit.

FIGURE 3. Geographic distribution of Chromolaena medullosa.