Exallosperma longiflora De Block, 2018

Block, Petra De, Rakotonasolo, Franck, Ntore, Salvator, Sylvain G. Razafimandimbison, & Janssens, Steven, 2018, Four new endemic genera of Rubiaceae (Pavetteae) from Madagascar represent multiple radiations into drylands, PhytoKeys 99, pp. 1-66 : 1

Exallosperma longiflora De Block sp. nov. Figs 2A-C , 4 , 5 , 9A-D, M

Diagnosis.

Differing from Homollea septentrionalis De Block by the size and shape of the leaves of the first order bracts (broadly ovate to orbiculate, 5.5-9.5 × 4.2-9.5 cm vs. broadly ovate to ovate, 0.8-3.5 × 0.5-2.5 cm in H. septentrionalis ), the calyx tube and lobes which are glabrous inside (vs. densely sericeous), the lower number of ovules (3-4 vs. 4-6) and the different seeds (2 seeds with irregularly distributed surface ridges, ca. 8 × 5.5 mm vs. 2-6 seeds with smooth surface, ca. 4.5 × 2.5-3 mm).

Type.

MADAGASCAR. Antsiranana Province, Analamerana, bank of Irodo river, close to Irodo camp, 8 Jan. 2002 (fl.), De Block, Rakotonasolo & Randriamboavonjy 1132 (holotype: BR!; isotypes: BR!, G!, K!, MO!, P!, TAN!, UPS!) .

Shrub, up to 5 m tall. Young shoots bisulcate, brown, densely covered with erect hairs, rapidly becoming corky with loss of pubescence; older branches brown or greyish-brown, corky and somewhat flaking. Leaves often immature at time of flowering, 7-12 × 5.5-8.5 cm, ovate or elliptic, more rarely broadly elliptic or broadly ovate (but leaves of first order bracts broadly ovate to orbiculate); blades papyraceous, drying brown to dark brown, not discolorous, densely covered with erect hairs on both surfaces; base cordate, rounded, truncate or unequal; apex acuminate, acumen 2-15 mm long; midrib and secondary nerves raised on the lower leaf surface; midrib impressed especially in the basal half on the upper leaf surface; 8-12 secondary nerves on each side of the midrib. Petioles densely covered with erect hairs, 10-25 mm long (but shorter in leaves of first order bracts). Stipules caducous, covered with erect hairs along the base and the keel outside but rapidly becoming corky and losing the pubescence; stipules of vegetative nodes with sheaths 1.5-2.5 mm long and awns 1.5-3 mm long, those of inflorescence-bearing nodes ovate with acute or shortly acuminate tips, 4-8 mm long. Inflorescences consisting of 3-12 flowers, 1-2 × 1-2 cm; anthesis asynchronous within inflorescence; all inflorescence parts (peduncle, axes, pedicels, bracts and bracteoles) densely covered with erect hairs; peduncle 1-3 cm long; first order axes 3-10 mm long; first order bracts with stipular parts triangular and leaves broadly ovate to orbiculate, 5.5-9.5 × 4.2-9.5 cm, with strongly cordate or cordate bases and petioles 3-6(-10) mm long; higher order bracts linear, up to 1.6 cm long; bracteoles opposite on the pedicel just below the ovary, linear, 0.4-1 cm long. Flowers sessile or shortly pedicellate, pedicels 0-2 mm long. Calyx green, densely covered with erect hairs outside; tube ca. 1 mm long, glabrous and without colleters inside; lobes narrowly triangular, 12-16 × 1-1.5 mm (but shorter in young buds), densely covered with appressed hairs at the base and spreading or erect hairs in the upper half inside, bases not overlapping but closely joining, tips acute. Corolla tube 2.7-3.6 cm long, ca. 1.5 mm in diameter at the base, c. 3.5 mm in diameter at the throat, densely covered with erect hairs outside, upper half densely covered with erect hairs inside with pubescence continuing in the throat and on the base of the corolla lobes; lobes elliptic, 9-11 × ca. 3.5 mm, sparsely to moderately covered with erect hairs outside, densely covered with erect hairs at the base inside, margins densely ciliate, tips acute to apiculate. Anthers sessile, inserted in the sinuses of the corolla lobes 2-2.5 mm below the level of the throat, included in the corolla tube except for the very tips, 3-3.5 mm long. Ovary ca. 1.5 mm long, green, densely covered with erect hairs. Style and stigma white, exserted from the corolla tube for 2-5 mm at anthesis, style glabrous or with a few long spreading hairs in the upper half; stigma slender, papillae present on the inner surface of the free tips, longitudinal papillate lines running down for up to 16 mm, but papillae absent just below the tips. Fruits 7-10 × 5-8 mm (persistent calyx not included), moderately to densely covered with erect hairs, drying black and glossy when ripe; seeds ca. 8 × 5.5 × 3 mm, dark brown.

Habitat.

Lowland dry deciduous and semi-deciduous forest on limestone; alt. 0-450 m.

Distribution.

Exallosperma longiflora is only known from the northernmost tip of Madagascar in the Sava and Diana Regions. Fig. 14A .

Phenology.

Flowering: January-February; Fruiting: April.

Critical note.

Exallosperma resembles the Madagascan endemic Homollea by the pedunculate, pauciflorous, pseudo-axillary inflorescences and the pentamerous flowers with relatively long corolla tubes and long, narrow calyx lobes. Exallosperma is characterised by the Terminalia -branching pattern, the large, broadly ovate to orbiculate leaves of the first order bracts, the basally attached placentas from which 3-4 collateral ovules arise, the fruit containing 2 stony pyrenes, each with a laterally flattened ovoid seed with irregularly distributed surface ridges formed by elongation of the exotesta cells and by the pollen with psilate tectum. Exallosperma longiflora may be confused with Homollea septentrionalis , which it resembles by the dense pubescence on vegetative and reproductive organs, the pauciflorous inflorescences, the long flowers with tapering corolla lobes and the long, linear calyx lobes. The two species can be distinguished by the size and shape of the leaves of the first order bracts (broadly ovate to orbiculate, 5.5-9.5 × 4.2-9.5 cm in Exallosperma longiflora vs. broadly ovate to ovate, 0.8-3.5 × 0.5-2.5 cm in H. septentrionalis ), the pubescence of the calyx tube and lobes inside (glabrous vs. densely sericeous), the number of ovules (3-4 vs. 4-6) and the different seeds (2 seeds with irregularly distributed surface ridges, ca. 8 × 5.5 mm vs. 2-6 seeds with smooth surface, ca. 4.5 × 2.5-3 mm).

Preliminary IUCN assessment.

Endangered: EN B1ab(i, ii, iii, iv) + 2ab(i, ii, iii, iv). The extent of occurrence (EOO) of Exallosperma longiflora is estimated to be 1,791 km2 and its area of occupancy (AOO) 54 km2, which both comply with the criteria for the Endangered category under sub-criteria B1 and B2. The species is known from seven collections, all but two of these collected after the year 2000, reflecting the intensified collection effort in northern Madagascar during the last 20 years. Exallosperma longiflora occurs in four locations, three of which are within protected areas, notably Réserve Spéciale d’Andrafiamena (which includes Analamerana), Loky Manambato (Daraina) and Montagne de Français. The main threat to E. longiflora is decline of its habitat both inside and outside the protected areas as a result of slash-and-burn agriculture, logging for timber and charcoal and burning to favour the growth of young grass for the grazing of cattle. Furthermore, traditional mining for gold is a serious threath in the area ( Rakotondravony 2009; Nusbaumer et al. 2010). Based on the above information, the species is listed as Endangered.

Additional specimens examined.

MADAGASCAR. Antsiranana Province: Montagne des Français, plateau supérieur de l’Anosiarivo, 28 Jan 1966 (fl.), Capuron 24425-SF (BR, P, TEF); Massif de l'Ankitakona , 25 Apr 1966 (fr.), Capuron 24663-SF (BR, P, TEF); Analamerana , bank of Irodo river , close to Irodo camp, 6 Jan 2002 (fl.), De Block , Rakotonasolo & Randriamboavonjy 1080 (BR, MO, P, TAN, UPS); Sava , sous-préfecture de Vohemar, commune rurale de Daraina, Daraina , forêt d’Ambilondomba, W of Ambilondomba, 300 m S du point côté 341, 150 m, 8 Mar 2003 (fr.), Gautier, Wohlhauser & Nusbaumer 4257 (BR, G, K); Sava, sous-préfecture de Vohemar, commune rurale de Daraina, Daraina, forêt de Solaniampilana-Maroadabo, à 700 m du point côté 608, au 85°, 437 m, 2 Feb 2006 (fl.), Nusbaumer & Ranirison 1992 (BR, G); Sava, sous-préfecture de Vohemar, commune rurale de Daraina, Daraina, forêt de Solaniampilana-Maroadabo, à 750 m du point côté 608, au 205°, 328 m, 4 Feb 2006 (fl.), Nusbaumer & Ranirison 2151 (G) .

Figures

Figure 2. Exallosperma and Helictosperma. A-C Exallosperma longiflora: A flowering branch B inflorescence C infructescence from herbarium specimen Gautier et al. 4257 D Helictosperma poissoniana, flowering branch E, F Helictosperma malacophylla: E inflorescence F detail of inflorescence. Photographs: P. De Block (A, D), S. Dessein (E, F), L. Nusbaumer (B, C, ©: Conservatoire et Jardin botaniques de la Ville de Geneve).

Figure 4. Exallosperma longiflora. A habit B stipules C inflorescence D bracteole, ovary and calyx E corolla and stigma F longitudinally opened flower, showing the position of stamens and style G stigma H placenta and ovules, abaxial view I fruit (with bracteole). A-G Capuron 24425 - SF H De Block et al. 1132 I Capuron 24663 - SF.

Figure 5. Exallosperma longiflora: pyrene and seed. A fruit with exocarp and mesocarp removed, showing two pyrenes B abaxial view of pyrene, showing apical preformed germination slit C adaxial view of pyrene, showing apical preformed germination slit and open centre D lateral view of seed, showing irregular ridges on the seed surface E cross-section through pyrene and seed, showing the adaxial opening of the pyrene, the entire endosperm and the irregular ridges formed by strongly elongated exotesta cells F longitudinal section of seed, showing the embryo position. A-F Capuron 24663 - SF.

Figure 9. Pollen of Exallosperma and Helictosperma. A-D, M Exallosperma longiflora E-H, N Helictosperma malacophylla I-L H. poissoniana. A, E, I polar view B, F, J equatorial view C, G, K mesocolpium D, H, L ectoaperture M, N pollen grain wall. A, M Nusbaumer & Ranirison 1992 B-D De Block et al. 1132 E-H, N Phillipson 3068 I-L Leandri 573.

Figure 14. Distribution maps. A Exallosperma longiflora B Helictosperma malacophylla C H. poissoniana D Pseudocoptosperma menabense E Tulearia splendida F T. capsaintemariensis.