Memecylon ourantherum R.D. Stone, 2022

Stone, Robert Douglas, 2022, Ten new species of Memecylon (Melastomataceae) from Madagascar, Candollea 77 (1), pp. 81-103 : 98-100

Memecylon ourantherum R.D. Stone , sp. nov. ( Fig. 10 ).

Holotypus: MADAGASCAR. Reg. Analanjirofo [Prov. Toamasina]: PN Mananara-Nord, forêt d’Ibanda, PK 12 d’Antanambe, 12.II.1990, fl., Raharimalala 266 (2-part specimen: P [ P00516019 , P00516020 ]!) .

Affine Memecyloni majori R.D. Stone, sed ab eo laminis foliaribus iterum majoribus 10–13 × 4–5.5 cm (non 6–9 × 2.3–3.5 cm) basaliter rotundatis subcordatisve (non cuneatis) ad apicem acumine plerumque acuto 15– 20 mm longo (non obtuso 6.5–14 mm) et floribus aliquantum majoribus corolla in alabastro 4 mm (non 2.5 mm) longa, petalis 4.5 mm (non 3 mm) longis, antheris 4 mm (non 3 mm) longis, antherae connectivo ultra glandem dorsalem 2.5 mm (non 1.5 mm) producto differt.

Shrubs evergreen, 2– 6 m high; young branchlets terete, with dark brown to blackish bark peeling off in elongaterectangular strips to reveal whitish inner bark; older branchlets c. 3 mm in diam. except for thickened nodes, remaining rather slender well below leaves; internodes 3.5–6.5(–7.3) cm long. Leaves coriaceous, petiolate, dark green and dull on adaxial surface, abaxial surface dull brown in dried material; petioles distinct but short and thick, 1–2.5 × 2 mm, flattened adaxially; blades elliptic to narrowly elliptic, 10–13 × 4–5.5 cm, base narrowly rounded to subcordate, apex ± caudate-acuminate, acumen (3–) 15–20 mm long, acute (in some leaves short and obtuse); midnerve clearly visible, impressed on adaxial surface; transverse veins c. 10 pairs faintly prominent on both surfaces in dried material, departing at an acute angle then oblique relative to midnerve, straight or sometimes forked, confluent with similarly weak intramarginal nerves. Cymes up to 2 cm long, 3–5-flowered, solitary or in fascicles of 2– 3 at nodes below leaves, 1–2 times branched; peduncles 2–10 mm long, robust, compressed; secondary axes 3–5 mm long, quadrangular; additional axes similar but shorter; bracts narrowly triangular, c. 1 mm long, acute, early deciduous; true pedicels short, c. 0.5 mm long. Flowers borne individually at ends of inflorescence axes; hypantho-calyx obconic to campanulate, 3 × 4 mm, margin truncate but with four V-shaped sinuses c. 0.5 mm deep; corolla in bud narrowly conical-acute, 4 mm long; petals reportedly whitish, ovate-acuminate, 4.5 × 1.75 mm, acumen c. 2 mm long; staminal filaments c. 4.5 mm long; anthers c. 4 mm long, thecae positioned at anterior end, dorsal oilgland c. 0.5 mm behind thecae, posterior extremity of connective caudate-acuminate, extending 2.5 mm past gland; style 10 mm long; epigynous chamber with 8 radial, membranous, interstaminal partitions, each partition also extending into a narrow ridge or crest c. 0.5 mm high adjacent to stylar scar. Fruits globose to ovoid-globose, 8 mm in diam.; calycinal crown appressed to summit of ovary.

Etymology. – The epithet ourantherum is a compound derived from the Greek noun ourá meaning “tail” and the noun anthera meaning “anther”. It functions as an adjective and means “tailed-anther”, in reference to the characteristic anthers of this species.

Distribution and ecology. – Northeastern Madagascar, known only from two collections made in the Ibanda forest c. 25 km to the west and inland from the coastal town of Mananara Avaratra. The soil is lateritic (i.e. ferralitic), according to the collector. Elevation c. 280 m.

Conservation status. – Memecylon ourantherum is known from a single location with an estimated AOO of 4 km ². Based on the latitude and longitude coordinates provided by the collector, this locality is outside the boundary of the Mananara-Nord National Park and remains unprotected. Anthropogenic pressures, especially extensive slash-and-burn agriculture, are continuing even within the protected area and have contributed to deforestation around the park’s periphery ( GOODMAN et al., 2021). Memecylon ourantherum is thus provisionally assessed as “Critically Endangered” [CR B2ab(iii)] in accordance with the IUCN Red List Categories and Criteria ( IUCN, 2012). With additional field-work, this species may eventually be found to occur within the park boundary.

Notes. – Memecylon ourantherum belongs to a group of montane species including M. subsessile , M. pedunculatum , M. centrale , and the newly described M. majus (see above) defined by their branchlets with brownish-black bark soon exfoliating in narrow, longitudinal strips to reveal whitish inner bark, as well as the character of flowers and fruit short-pedicellate to ± sessile above the peduncle ( STONE & CALLMANDER, 2011). It is most similar to M. majus , differing from that species in having larger leaves 10–13 × 4–5.5 cm (vs. 6–9 × 2.3–3.5 cm) that are basally rounded to subcordate (vs. cuneate) and apically acute (the acumen ± acute and 15–20 mm long vs. obtuse and 6.5–14 mm), larger flowers with corolla in bud 4 mm long (vs. 2.5 mm), petals 4.5 mm long (vs. 3 mm), anthers 4 mm long (vs. 3 mm), and anther connectives extending beyond the dorsal gland by 2.5 mm (vs. 1.5 mm). The two species are also wholly allopatric, with M. majus occurring further north and with its nearest known locality separated from M. ourantherum by a distance of c. 150 km. The fruits of M. ourantherum are very much like those of M. pedunculatum .

In addition to the two sheets in P identified below as paratypes of Memecylon ourantherum , there is a third sheet [P00516201] labeled as Raharimalala 1089 but with a different collecting date (20.VII.1990) and with material clearly belonging to Memecylon sect. Pseudonaxiandra sensu JACQUES-FÉLIX (1985 a) . It remains undetermined to species pending further study.

Additional specimens examined. – MADAGASCAR. Reg. Analanjirofo [Prov. Toamasina]: PN Mananara-Nord, forêt d’Ibanda, 280 m, 27.II.1990, fr., Raharimalala 1089 ( P [ P00516202 , P05320686 ]) .

Figures

Fig. 10. – Memecylon ourantherum R.D. Stone. A. Leafy branch; B. Flowering branch; C. Leaf; D. Floral bud; E. Flower at anthesis; F. Petal; G. Stamen; H. Section of fruiting branch; I. Fruit. [A, B, D–G: Raharimalala 266, P;C, H, I: Raharimalala 1089, P] [Drawing: S. Burrows]