Humbertacalia diffusa (Baker) J. Calvo, Rabarim. & Callm., 2023

Rabarimanarivo, Marina N., Callmander, Martin W. & Calvo, Joel, 2023, Synopsis of Humbertacalia (Compositae), a genus endemic to Madagascar and Réunion, Adansonia (3) 45 (7), pp. 93-113 : 102

5. Humbertacalia diffusa (Baker) J. Calvo, Rabarim. & Callm. , comb. nov., stat. nov.

Senecio exsertus var. diffusus Humbert , Notulae Systematicae 15 (4): 371 ( Humbert 1959).

— Typus: Madagascar. Atsinanana Region [Prov. Toamasina], Lamandra, environs de Foulpointe, N. de Tamatave , [17°41’S, 49°31’E], 12.XI.1881, fl., Humblot 81 (lecto-, designated here, P [ P00727182 ]!; isolecto-, P [ P00727183 ]!) .

ETYMOLOGY. — The epithet diffusa probably refers to the lax synflorescences that this species displays.

VERNACULAR NAMES. — Unknown.

DISTRIBUTION AND ECOLOGY. — Humbertacalia diffusa comb. nov., stat. nov. occurs in humid bioclimate, in lowland moist evergreen forest of northeastern Madagascar (Atsinanana and Sava Regions), at low elevations c. up to 100 m.

CONSERVATION STATUS. — Humbertacalia diffusa comb. nov., stat. nov. has an area of occupancy (AOO) of 8 km 2 and two locations with respect to the most serious plausible threat of shifting agriculture. Its known distribution does not include any of the protected areas and we infer continuing decline in its AOO, habitat quality, number of subpopulations and number of the mature individuals as well. Therefore, H. diffusa comb. nov., stat. nov. is assessed as “Endangered” [EN B2ab(ii,iii,iv,v)] according to IUCN Red List Categories and Criteria ( IUCN 2012).

ADDITIONAL SPECIMENS EXAMINED. — Madagascar. Sava Region [Prov. Antsiranana]: Antanandavahely, S / P d’Antalaha, [15°17’S, 50°20’E], 16.VII.1966, fl. & m. fr., Jacquemin 64- J ( P [ P 04428413]); ibid. loco, m. fr., Rakotozafy 515 ( TAN).

DESCRIPTION

Leaves petiolate; leaf laminas 5.4-6.1 × 2-2.6 cm, lanceolate to narrowly elliptic, base cuneate to attenuate (sometimes oblique), apex acute, margins entire or remotely mucronatedenticulate to shallowly and distantly sinuate, glabrescent (initially arachnoid) on both surfaces, venation pinnate (usually conspicuous on both surfaces), rather chartaceous; petioles up to 1.5 cm long. Synflorescences axillary and terminal, thyrsoid-paniculiform. Capitula long-pedunculate (peduncles 6-15 mm); involucres campanulate, arachnoid-floccose (at least at base); involucral bracts 12-13, 2.9-3 × 0.7-1 mm; supplementary bracts 4-6, 0.7-1.5 mm long. Florets 10-20, 3-4 mm long; corollas tubular, 5-lobed, whitish; anther bases caudate, as long as or slightly longer than filament collar; style branches truncate to obtuse with a crown of sweeping trichomes. Achenes 1.5-2 × c. 0.5 mm, rather cylindrical, 8-10-ribbed, glabrous, straw-coloured to brownish; pappus 3-4 mm long, whitish.

NOTES

This taxon was originally described as a variety of Senecio exsertus ( Humbert 1959) , the latter being a replacement name for Cacalia racemosa (synonym of Humbertacalia racemosa ) under Senecio , but later placed in synonymy under S. volutus ( Humbert 1963) , which is here referred to as a synonym of Humbertacalia apocynifolia comb. nov. The indumentum of the synflorescence branches and leaves, as well as the number and length of the involucral bracts, matches well the overall characters of H. apocynifolia comb. nov. but it remarkably differs in the synflorescence architecture (capitula long-pedunculate not arranged in glomerules in H. diffusa comb. nov., stat. nov. vs capitula sessile to subsessile arranged in glomerules in H. apocynifolia comb. nov.). Since the synflorescence architecture appears to be a useful discriminating character in this plant group, we consider it appropriate to treat this taxon at the specific rank. Because of the pedunculate capitula, this species might also be confused with H. racemosa , but this latter species has 2-5 mm long peduncles (vs 6-15 mm long in H. diffusa comb. nov., stat. nov.), 8(-9) involucral bracts, 3.6-4 mm long (vs 12-13 involucral bracts, 2.9-3 mm long in H. diffusa comb. nov., stat. nov.) and glabrous leaves and synflorescence branches (vs initially arachnoid leaves and floccose synflorescence branches in H. diffusa comb. nov., stat. nov.).