Holotypus: Madagascar. Reg. SAVA [Prov. Antsiranana]: Daraina, forêt d'Antsahabe, [13°13′S 49°33′E], 390 m, 30.IV.2004, fl., Ranirison 749 (G [G00028103]!; iso-: TEF image!, P).

Kalanchoe darainensis D.-P. Klein & Callm. differs from other representatives of Kalanchoe subg. Kalanchoe by its dense indumentum of medium to long glandular hairs, covering all parts of the plant except flowers and bracteoles, its basally near-ligneous stems, soboliferous above, developing a single, erect, terminal inflorescence per rosette, rarely two, with a single peduncle each, composed in the apical half of a single node, its indistinct calyx tube, narrowly lanceolate and acute sepals, a corolla tube gradually constricted above to a subcylindrical throat in the apical half, with scarlet red, erect flowers and anthers dressed with flattened spheroid connective glands.

Plants small, perennial, rosulate and succulent, 8.5–13.5 cm high, mostly erect, creeping to decumbent at base, soboliferous, bearing one to few lateral basal shoots, almost entirely densely covered with medium to long glandular hairs. Stems 2.5–3.5 mm in diameter, terete, basally near-ligneous and without indumentum when mature, bearing roots and lateral shoots, densely covered with medium (0.5–1 mm) white-brownish glandular hairs. Leaves opposite, decussate, succulent, light bright green to olive with slightly reddish margins, arising from a rosette bearing up to 6 pairs of leaves, entirely covered with whitish to brownish, medium (0.5 mm) to long (1.9 mm) glandular hairs, long-petiolate to subsessile; petioles 1.5–21.5 × 0.5–4 mm, subcylindrical, somewhat flattened above, convex below, broadening towards the leaf base, densely covered with whitish to brownish, short (0.2 mm) to medium (1 mm) glandular hairs. Leaf blades 6–50 × 4–51 mm, ovate, elliptic to orbicular, sometimes wider than long, adaxially canaliculate along the midrib, densely covered with long (up to 1.9 mm) whitish glandular hairs; tip obtuse-rounded; base obtuse to ± rounded or near-truncate, often oblique; margins irregularly wide-sinuate to wide-crenate. Inflorescences a few- to many-flowered dichasial cyme with up to 3 secondary branches bearing up to 31 flowers, erect, typically one terminal inflorescence per rosette, rarely two, sparsely covered with medium (up to 0.5 mm) whitish-brownish glandular hairs up to the second node of the inflorescence; peduncle 65–100 × 0.4–1.5 mm, terete, thinning apically, bearing 1–few pairs of peduncular bracts, apical half composed of a single node, densely covered with medium (up to 0.5 mm) whitish-brownish glandular hairs peduncular bracts 1.6–5 × 0.5–3 mm, borne in the lower third or middle of the peduncle, subsessile, densely covered with medium (up to 0.5 mm) whitish-brownish glandular hairs, tip obtuse, base cuneate, margins irregularly sinuate to crenate. Flowers 8–10 × 2.5–4 mm, erect. Bracts 1.2–1.3 × 0.25–0.4 mm, sessile, lanceolate, slightly incurved, apically acute, sparsely glandular hairy. Pedicels 2–2.5 × 0.3–0.7 mm, erect, widening towards the flower. Bracteoles 0.8–1.5 × 0.1–0.2 mm, sessile, narrowly lanceolate, incurved, apically acute, glabrous. Calyx tubes 0.1–0.2 mm long, indistinct, green. Sepals 1–1.9 × 0.20–0.65 mm, free, sometimes slightly adpressed to corolla tube in lower 1/10, narrowly lanceolate, apically acute. Corolla tubes 6–8 mm long, at its widest part 1.5–2 mm, scarlet red, ± 4-angled where it is widest and adpressed against the carpels, gradually constricted above to a subcylindrical throat, very slightly widening towards the petals. Petals 2–3.5 × 2 mm, ovate-obovate, apex obtuse, short-mucronate (0.1 mm long). Stamens 8, arranged in two rows, 4 stamens each, fused to the corolla tube internally for the most part, free segments short, anthers of upper row at most reaching to slightly exserting the corolla mouth; upper filaments (oppositipetalous) inserted at c. 6.5 mm above corolla base, free for 0.3–0.5 mm; lower filaments (alternipetalous) inserted at c. 5 mm above corolla base, free for 1–1.3 mm. Anthers dull brownish-yellow, each locule (theca) 0.35 × 0.5 × 0.1 mm, elliptic, base emarginate, apex rounded, dressed with a flattened spheroid connective gland; connective gland erythrocyte-shaped, distinctly present only on the upper stamens, 0.3 × 0.3 × 0.05 mm. Pistils consisting of 4 carpels; carpels 4.5–6 × 1–1.4 mm, greatest width towards the middle, convergent; styles 1.2–1.5 mm long; stigmas very slightly capitate. Scales 2.2–2.5 × 0.2 mm, long and thin, flattened, adpressed to carpel, whitish, ligulate /strap-shaped, apex truncate to rounded. Seeds 0.5 × 0.15 mm, brown, longitudinally furrowed (striate).

Distribution, ecology and phenology. – Kalanchoe darainensis is known only from the Antsahabe forest in the Loky-Manambato region (Daraina) in northeastern Madagascar (Fig. 1). Being situated between the Eastern humid and the Western dry phytogeographical domains, with elevation levels partially resembling those of the Central domain, this area comprises particularly diverse vegetation types (Ranirison et al., 2018). Only four individuals of the new species were found among all the localities visited during a vegetation study, which included more than 54,000 records of plant occurrences in the 10 main forest areas of that region (Nusbaumer, 2011). These individuals were observed at elevations between 390 and 900 m where the annual mean precipitation reaches 1400 – 1450 mm and annual mean temperatures vary from 17.5–21° C, depending on the elevation level (Nusbaumer, 2011). Kalanchoe darainensis grows on the lower slopes of rocky outcrops on raw mineral soils (lithic erosion soils on leucocratic granite or skeletal soils on cristalin domes) in rupicolous vegetation mainly surrounded by primary mesophilous and ombrophilous forest (Ranirison et al., 2018), but also by matrix habitats on a ridge covered with sparse vegetation with a low canopy. The rupicolous vegetation reaches heights of 1 m with occasionally emerging treelets up to 4–5(–8) m tall. The most frequently recorded species occurring with K. darainensis include: Artabotrys darainensis Deroin & L. Gaut. (Annonaceae), Aulotandra trigonocarpa H. Perrier (Zingiberaceae), Chasechloa humbertiana A. Camus (Poaceae), Doryopteris cordifolia (Baker) Diels (Pteridaceae), Dracaena reflexa var. linearifolia Baker (Asparagaceae), Emilia humifusa DC. (Asteraceae), Eugenia viguieriana H. Perrier (Myrtaceae), Pandanus cf. grallatus B.C. Stone (Pandanaceae) and Xerophyta sp. (Velloziaceae).

Other species of Kalanchoe collected in the Loky Manambato region include K. aff. miniata Hilsenb. & Bojer ex Tul., K. maromokotrensis Desc. & Rebmann, K. pinnata (Lam.) Pers. and K. porphyrocalyx (Baker) Baill.

Kalanchoe darainensis was collected in flowers between April and October.

Conservation status. – While Kalanchoe darainensis is known only from four collections representing four locations (sensu Iucn, 2012), it is situated within a large block of forest in the Loky-Manambato protected area. No future decline is expected in terms of Area of Occupancy (AOO), Extent of Occurrence (EOO), or quality of habitat. We therefore assign a preliminary risk of extinction status of “Least concern” [LC] using the IUCN Red List Categories and Criteria (Iucn, 2012).

Notes. – Kalanchoe darainensis is morphologically most similar to K. blossfeldiana and K. globulifera (Table 1). The two latter species are restricted to the high-altitude humid forests of the Tsaratanana mountain range, c. 100 km south-west from Daraina. Like K. darainensis, these species are perennial, small-sized, soboliferous, rosulate plants with simple leaves and a subcylindrical corolla-throat. Kalanchoe blossfeldiana and K. darainensis share the same flower characters, i.e. the scarlet red flower color and the petals being ovate-obovate, with an obtuse, mucronate apex. Kalanchoe globulifera and K. darainensis both produce few- to many-flowered dichasial cymes, are at least partially glandular pilose and are dressed with connective glands on the anthers. Among the northern representatives of Kalanchoe subg. Kalanchoe in Madagascar, a scarlet red flower color is unique to K. blossfeldiana and K. darainensis.

Additional specimens examined. – Madagascar. Reg. SAVA [Prov. Antsiranana]: Daraina, massif d'Antsahabe, 13°13′S 49°33′E, 620 m, 16.X.2004, Callmander et al. 241 (G, K, MO, P, TEF); ibid. loco, 13°13′S 49°33′E, 900 m, 6.XII.2004, Gautier & Nusbaumer LG 4843 (G, K, MO, P, TEF); ibid. loco, 13°13′S 49°33′E, 560 m, 3.XI.2005 Razafitsalama et al. 771 (MO, P, TAN).