Homollea leandrii Arènes

Block, Petra De, 2018, Revision of the Madagascan endemic Homollea (Rubiaceae - Pavetteae), with description of two new species, European Journal of Taxonomy 423, pp. 1-24 : 9-10

Homollea leandrii Arènes

Figs 2 , 6A

Notulae Systematicae 16: 15, f. 3 (9 –13) ( Arènes 1960). – Type: Madagascar, Mahajanga Province, Melaky Region, district Antsalova , Réserve Naturelle Intégrale de Bemaraha , 8 Dec. 1952 (fl), coll. ignot. 4680-RN (holo-: P; iso-: P, TAN, TEF).

Other material studied

MADAGASCAR: Mahajanga Province: Melaky Region, Parc National de Bemaraha , 50–135 m, 10 Jul. 2006 (fr), Andriambololonera, Ramelison, Rakotonasolo, Andriamanampandry & Lanne 171 ( BR, MO, P); district Antsalova, National Park Tsingy de Bemaraha, near Ambodiria, route to Tsiandro, before Bevary , 115 m, 18 Mar. 2004 (fr), Davis & Rakotonasolo 3132 ( BR, K, TAN); Réserve Naturelle Intégrale de Bemaraha, Tsiandro , 10 –12 Feb. 1953 (fr), Leandri 884 ( P); aux environs de Tsiandro , 500– 600 m, 25 Nov.–3 Dec. 1952 (fl), Leandri, Capuron & Razafindrakoto 1978 ( P); forêt de l’Antsingy, vers Ambodiriana, E d’Antsalova , 100–150 m, 9–10 Dec. 1952 (fl), Leandri, Capuron & Razafindrakoto 2094 ( BR, P, MO); forêt de Tsiampihy, près de la Réserve Naturelle Intégrale de Bemaraha , 0–20 m, 19 Dec. 1952 – 2 Jan. 1953 (fl), Leandri, Capuron & Razafindrakoto 2215 ( P); calcaires de l’Antsingy, vers Ambodiriana, E d’Antsalova , 100–150 m, 21–27 Jan. 1960 (fl), Leandri & Saboureau 2757 ( BR, G, K, MO, P); calcaires de l’Antsingy, vers Ambodiriana, E d’Antsalova , 100–150 m, 21–27 Jan. 1960 (fl), Leandri & Saboureau 2764 ( P); Beanka, partie centrale, Ambinda-Nord , 227 m, 12 Feb. 2012 (fl), Rakotozafy, Bolliger & Hanitrarivo 48 ( BR, G).

Description

Small shrub, 2–3 m tall; vegetative and reproductive parts glabrous (externally); young shoots brown, smooth; older shoots fawn or pale beige, glossy, flaking. Leaves with petioles 0.5–1.5 cm long; blades elliptic, ovate or obovate, 5–12.5 × 2–5 cm, coriaceous, drying glossy and green or brownish above, glossy and somewhat paler below; apex acuminate, acumen 0.4–1.2 cm long; base attenuate; secondary veins 5–10 on each side of midrib; ciliate pit domatia present; stipules 0.6–1 cm long, basal cone 2.5–5 mm long, free parts of sheaths 2–4.5 mm long, ovate with acuminate tips, acumen 1–2 mm long. Inflorescences 3–12-flowered; peduncle 2–12 cm long; first order axes up to 2 mm long but often absent; first order bracts consisting of 1.5–4 mm high, broadly ovate or broadly triangular, keeled sheaths with acuminate tips and blades ovate or broadly ovate, (1.2–)2–6.5 × 1–3.5 cm with rounded to truncate bases and 1–3 mm long petioles; higher order bracts usually absent, if present, then strongly reduced, triangular, up to 0.5 mm long; bracteoles absent. Flowers shortly pedicellate, pedicels up to 2 mm long; calyx tube 1–2 mm long, glabrous and without colleters inside; calyx lobes (6–)8–12 × 0.5–1.5 mm, sparsely ciliate at the base outside (trichomes usually absent in fruiting stage), glabrous inside, tips obtuse to rounded; corolla tube (6 –) 23–26 mm long, densely villose in the upper third inside; corolla lobes 8–13 × 2–3 mm, tips obtuse to rounded; anthers 4–5.5 mm long, exserted for ca 3 mm from corolla tube at anthesis, inserted ca 0.5 mm below the level of the throat; ovary 1.25–1.5 mm long, sometimes faintly ribbed longitudinally (when dry); (2–)3 ovules per locule; stigma exserted from corolla tube for (3–) 6–11 mm at anthesis, receptive zone 10–16 mm long. Fruits 5–7.5 × 6.5–8 mm (persistent calyx not included); pyrenes stony, with four longitudinal preformed germination slits (two along the lines of fusion of the two locules and two perpendicular to those), breaking up into individual dispersal units (ca 4) formed by part of the pyrene wall and part of the stony septum, each containing a single seed; seeds ca 4 per fruit, ca 3 × 3.5 mm.

Distribution

Known from the Melaky Region in western Madagascar (Mahajanga Province): only collected in the vicinity of Antsalova and Tsingy de Bemaraha ( Fig. 6A ).

Habitat and phenology

Lowland dry semideciduous or deciduous forest, on limestone, alt. 0– 600 m. Flowering: December– January; fruiting: February–July.

IUCN status

Endangered: EN B1ab(i,ii,iii,iv,v) + 2ab (i,ii,iii,iv,v). The extent of occurrence (EOO) of H. leandrii is estimated to be 4,160 km 2, and its area of occupancy (AOO) 63 km 2 using a cell width of 3 km. Most of the specimens of this species were collected in the 1950s and 1960s. Only three specimens date from after the year 2003, two of these from inside the Tsingy de Bemaraha National Park, the third from Beanka forest. The species is present in two protected areas: the Tsingy de Bemaraha Strict Nature Reserve and the adjacent Tsingy de Bemaraha National Park, which have been protected since 1927. But, except for the inaccessible tsingy, the reserves are threatened by fires which are set each year in the dry season in order to favour the growth of young grass for the grazing of cattle ( Nicoll & Langrand 1989; Rasoloarison & Paquier 2008). Habitat loss as a result of bush fires is also a serious threat for H. leandrii outside the protected areas. Considering these threats and the fact that the species is distributed in only five locations, H. leandrii is assessed as Endangered (EN).

Notes

Only few specimens with mature flowers were collected. The length of the corolla tube is very variable. It would seem that well-developed flowers have a corolla tube of 20–25 mm long, as is the case in the other Homollea species. However, the type collection, coll. ignot. 4680-RN, shows flowers with short (6–7 mm) and longer (16–22 mm) corolla tubes. In Leandri, Capuron & Razafindrakoto 2094 the corolla tubes are hardly longer than the calyx tube (corolla tubes 12 –15 mm long). Even in specimens with mostly well-developed flowers, such as Leandri & Saboureau 2757, rare shorter flowers can be found (corolla tube 16 mm vs 22–25 mm long in most flowers).

Figures

Fig. 2. Homollea leandrii Arènes. A. Flowering branch. B. Ovary and calyx. C. Detail of B showing the sparsely ciliate base of the calyx lobes. D. Corolla, stamens, style and stigma. E. Fruit. F. Pyrene, apical view. G. Pyrene, basal view. H. Dispersal unit, adaxial view. I. Seed, lateral view. Drawn by Mr. A. Fernandez.A–C from Leandri 2094 (P); D from coll. ignot. 4680-RN (P); E from Leandri 884 (P); F–I from Andriambololonera et al. 171 (BR).

Fig. 6. Distribution maps of Homollea. A. H. furtiva De Block, sp. nov. (★), H. leandrii Arènes (●) and H. longiflora Arènes (▲). B. H. perrieri Arènes (▲), H. SeptentrionaliS De Block sp. nov. (●) and unplaced material coll. ignot. 25309-SF (★).