Antherostele samarensis Obico & Alejandro, 2013

Obico, Jasper John A. & Alejandro, Grecebio Jonathan D., 2013, A new species of Antherostele (Urophylleae, Rubioideae, Rubiaceae) from Mt. Sohoton, Samar, Philippines, Phytotaxa 104 (1), pp. 53-57 : 54-56

Antherostele samarensis Obico & Alejandro , sp. nov. ( Fig. 1 )

Antherostele samarensis closely resembles A. callophylla but differs by the presence of petioles non canaliculate, stipules triangular, 2–4 × 2–3 mm with colleters distributed throughout the adaxial side, staminate calyx 5–7 mm long and 3– 4 mm in diam., pistillate calyx lobes 0.5–1 × 0.8–1 mm, and corolla lobes strongly reflexed.

Type:— PHILIPPINES. Samar: Mt. Sohoton foothills, Basey, Barangay Guirang , Sitio Wespal , 11° 23' 33"N, 125° 11' 51" E, 265 m, 26 January 2010, J.J.A. Obico & G.J.D. Alejandro 25107 (holotype USTH!; isotypes L!, NY!, PUH!, US!).

Trees 3–5 m tall; bark light brownish-gray, smooth; branches with solid pith; young branches somewhat compressed at distal internodes, subterete at lower internodes, glabrous; old branches light brown, glabrous. Stipules triangular, 2–4 × 2–3 mm, apex acute to obtuse, coriaceous, adpressed, glabrous outside, pilose and intermixed with colleters throughout inside, deciduous. Leaves glabrous; petioles 1.4–1.9 cm long, not canaliculate; blades elliptic, 10.5–12.7 × 4–6 cm, coriaceous, eucamptodromous, base acute to rounded, apex acuminate, light greenish-brown below when fresh, light green below when dry, with pit domatia at axils of secondary veins; midrib grooved, midrib and secondary veins prominulous; midrib and veins prominent; secondary veins 8–10 each side. Inflorescences axillary, usually paired, subsessile, 1–3 flowered; peduncles <1 mm long, glabrous; bracts 1–3, <1mm long, dry, brown; margin sparsely ciliolate. Staminate flowers: pedicels 1.1–1.5 cm long, distally puberulent towards the base; calyx tube 0.5–0.7 cm long, 0.3–0.4 cm in diam., truncate, dentate or slightly crenate, punctuate outside, glabrous or with a few hairs; corolla tube 1.1– 1.2 cm long, 2–2.8 mm in diam., relatively thin, with a ring of pubescent hairs at upper 1/3 of corolla tube inside, lobes (4–)5, 0.9–1.0 × 0.2 cm, strongly reflexed; stamens inserted at upper 1/3 of corolla throat; connective prominent (not dorsally keeled), without apical process; anthers 5–6 × 0.5–1 mm; ovary rudimentary; disc thin, glabrous; style 1–1.5 mm long, papillose; style branches 1.5 mm long, papillose. Pistillate flowers: calyx similar to that of staminate flowers except cup-shaped and lobed, 1–5 mm long, 3–4 mm in diam., glabrous outside, pubescent inside; lobes 5, 0.5–1 × 0.8–1 mm, triangular, pilose on margin and inside; corolla similar to those of staminate flowers except tube 3.5 mm long, 2.5–3 mm in diameter, lobes 4– 5 × 2.5–3 mm; staminodes insertion similar to that of staminate flowers, connective dorsally keeled, mucronate, antherodes 1.4 × 0.5 mm, basifixed, apex recurved; hypanthium ovoid, glabrous; ovary 5-locular; disc papillose; style 1.5–3 mm long, glabrous; style branches 1.5–2 mm long, papillose. Fruits subglobose, 6– 9 x 7–8 mm, glabrous; stalks 1.3–3 cm long, glabrous to puberulous; persistent calyx 3 mm in diam.; mesocarp 0.5–2 mm thick. Seeds ellipsoid, 0.4–0.5 × 0.3–0.45 mm, brown.

Distribution & Habitat:— Samar and Mindoro Islands; in forest understory, at 100–300 m, near river bank, steep valley slopes; on clay-loamy soils.

Etymology:— Refers to the type locality of this species.

Phenology:— Flowering in January; fruiting in April.

Additional specimens examined (paratypes):— PHILIPPINES. Mindoro: San Teodoro Island, at and above Subaan River , 13°22’N, 121°00’E, 300 m, 19 April 1986, C.E. Ridsdale 1186 (A!) . Samar: Mt. Sohoton, Basey, Barangay Guirang , Sitio Wespal , 26 January 2010, J.J.A. Obico & G.J.D. Alejandro 25108 (PUH!), 25112 (HUH!, K!, PUH!, USTH!); 11°21’ N, 125°10’ E, 100 m, 19 April 2010, J.J.A. Obico & G.J.D. Alejandro 25127 (PNH!, PUH!, USTH!); Catarman, Mt. Cansayao , 12 April 1951, M.D. Sulit PNH14446 (A!) .

Discussion:— Antherostele samarensis is characterized by the petioles non canaliculate, stipules triangular, 2–4 × 2–3 mm with colleters distributed throughout inside, staminate calyx 5–7 mm x 3–4 mm, pistillate calyx lobes 0.5–1mm × 0.8–1 mm, and strongly reflexed corolla lobes. It is most similar to A. callophylla , from which it is easily distinguished by the characters summarized in Table 1.

Antherostele samarensis is the second record of Antherostele in Mt. Sohoton from where A. grandistipula is also found. A. grandistipula differs from A. samarensis by having much longer leaves (12–23.5 cm long) and larger stipules (3–3.5 × 1–2 cm). A. samarensis is somewhat rare and thus far known only from Samar and Mindoro. It thrives in the forest understory, at 100–300 m elevation, near banks of creeks or rivers, and mountain slopes.

Figures

FIGURE 1. Antherostele samarensis A. Flowering branch. B. Axil of leaf veins with a domatium. C. Inflorescence at leaf axil. D. Staminate flower. E. Corolla of staminate flower longitudinally cut, showing syngenesious stamens. F. Staminate flower (corolla removed) in longitudinal section showing reduced, non-functional style (drawn from J.J.A. Obico & G.J.D. Alejandro 25127 by Nemesio B. Diego, Jr.)