Synopsis of Humbertacalia (Compositae), a genus endemic to Madagascar and Réunion Author Rabarimanarivo, Marina N. Missouri Botanical Garden, P. O. Box 3391, Antananarivo 101 (Madagascar) marina.rabarimanarivo@mobot.org Author Callmander, Martin W. Conservatoire et Jardin botaniques de Genève, ch. de l’Impératrice 1, C. P. 71, 1292 Chambésy (Switzerland) martin.callmander@ville-ge.ch Author Calvo, Joel Conservatoire et Jardin botaniques de Genève, ch. de l’Impératrice 1, C. P. 71, 1292 Chambésy (Switzerland) joel.calvo@ville-ge.ch text Adansonia 2023 3 2023-03-27 45 7 93 113 journal article 239621 10.5252/adansonia2023v45a7 cf3c1994-a819-4671-8e7d-348faa5d0ea4 1639-4798 7774939 2. Humbertacalia amplexifolia (Humbert) C. Jeffrey Kew Bulletin 47 (1): 83 ( Jeffrey 1992 ) . Senecio amplexifolius Humbert, Mémoires de la Société linnéenne de Normandie 25: 139, 303 ( Humbert 1923 ). — Typus: Madagascar . Diana Region [Prov. Antsiranana ], Mt. Tsaratanana , [ 13°57’S , 48°52’E ], 2000 m , XII.1912 , fl., Perrier de la Bâthie 2809 ( holo- , P[ P00498727 ]!) . ICONOGRAPHY. — Humbert (1963: 761 , fig. 139, 1-2, sub Senecio amplexifolius ). ETYMOLOGY. — The epithet amplexifolia describes the distinctive sessile leaves of this species. VERNACULAR NAMES. — Unknown. DISTRIBUTION AND ECOLOGY. — Humbertacalia amplexifolia is endemic to northern Madagascar (Diana Region), occurring in subhumid bioclimate and known only from the Tsaratanana massif, in montane ericoid thickets, on granitic or basaltic substrate, at elevation c. 2000 m . CONSERVATION STATUS. — Humbertacalia amplexifolia has a very restricted distribution with an area of occupancy (AOO) of 4 km 2 based upon a single locality from two historical collections within the Tsaratanana protected area. The remaining montane ericoid thickets in the vast summit plateau is scarce because of an accidental fire by a geological expedition at the beginning of the 20th century ( Gautier et al. 2018b ). Only a few vestiges remain, and therefore, the habitat of H. amplexifolia is in threat because of its vulnerability to further fire. On this basis, H. amplexifolia is assessed as “Critically Endangered” [CR B2ab(iii)] according to IUCN Red List Categories and Criteria ( IUCN 2012 ). ADDITIONAL SPECIMENS EXAMINED. — Madagascar . Diana Region [Prov. Antsiranana ]: Massif du Tsaratanana et haute vallée du Sambirano (Réserve naturelle n° 4), vers l’Antsasarotra, [ 13°57’S , 48°52’E ], 2000 m , XI-XII.1937, fl., Humbert 18319 ( G , P [ P02397556 , P02397557 , P04391737 ], TAN [ TAN001008 ]) . DESCRIPTION Leaves subsessile; leaf laminas 5-9 × 2-4.2 cm , lanceolate, base amplexicaul to semi-amplexicaul, apex acute to attenuate, margins dentate (teeth up to 3 mm deep), glabrous on both surfaces, venation pinnate (conspicuous on both surfaces, including tertiary veins), rather coriaceous; petioles very short (up to 2 mm long). Synflorescences axillary and terminal, corymbose-paniculiform. Capitula pedunculate (peduncles 2-8 mm long); involucres rather cylindrical, glabrous, somewhat swollen at base; involucral bracts 5, 3-3.6 × 0.8-1.3 mm ; supplementary bracts 3-4, 0.5-0.8 mm long. Florets 8-10, 4.3-4.5 mm long; corollas tubular, 5-lobed, whitish; anther bases sagittate, a quarter as long as filament collar; style branches obtuse with a crown of sweeping trichomes. Achenes 2.4-2.6 × c. 0.8 mm , rather cylindrical, c. 6-ribbed, glabrous, straw-coloured; pappus c. 3.8 mm long, whitish. FIG. 1. — Lectotype of Senecio exsertus var. abbreviatus Humbert, Decary 5226 (P00835897). NOTES This species is easily distinguished by its subsessile leaves with the lamina bases amplexicaul to semi-amplexicaul. These characters make this species unique within the genus that any confusion with the remaining taxa is unlikely.