Memecylon incisilobum R.D. Stone & I.G. Mona, 2017

Stone, Robert Douglas, Mona, Imercia Gracious & Ramdhani, Syd, 2017, Revised treatment of Mozambican Memecylon (Melastomataceae-Olisbeoideae), with descriptions of four new species in M. section Buxifolia, Phytotaxa 331 (2), pp. 151-168 : 152-157

Memecylon incisilobum R.D. Stone & I.G. Mona , sp. nov. ( Figs. 1 , 2 )

Type:— MOZAMBIQUE. Prov. Gaza: forest surrounding M-cel tower 11 km from Bilene on road to Macia, elevation 60 m, 25°11'31"S, 33°12'33"E, 28 October 2015, Burrows et al. 14765 (holotype BNRH!, isotypes CAS, K, LMA, MO, NH, NU!, PRE).

Evergreen understory tree up to 7 m tall; bark brownish gray, longitudinally fissured; young branchlets slender, quadrangular to narrowly quadrangular-alate; older branchlets terete, whitish gray, longitudinally fissured; nodes thickened; internodes between normal leafy nodes (2–) 3–5 (–6) cm long. Leaves subcoriaceous, dark green and glossy above, somewhat paler below; petioles 2.5–3 mm long; blades elliptic, (4.5–) 5–7 (–8.5) × (1.8–) 2.5–3.5 (–4.5) cm, cuneate at base (margins curved slightly inwards) and confluent with the petiole, ± broadly and obtusely acuminate at apex, the acumen (3–) 4.5–8.5 (–11) mm long (sometimes indistinct or with apex acute); midnerve clearly visible, impressed on the upper surface, ± prominent on the lower (especially toward the leaf base); one pair of lateral nerves faintly visible on both surfaces, curvilinear and 1.5–4 mm from the margin in the basal half of the blade; transverse veins ca. 5 pairs, faintly visible, oblique relative to the midnerve, prominent on both upper and lower surfaces in dried material. Cymes 1–9-flowered, solitary (rarely geminate) at the defoliated nodes of older branchlets, less often in the leaf axils and at the bracteate nodes alternating with those bearing fully developed leaves, occasionally borne terminally; peduncles (3–) 5–10 (–13) mm long; secondary axes slender, 1–5 in number, mostly 3.5–7 mm long; additional axes when present mostly 3–5.5 mm long; bracts rapidly deciduous. Flowers borne individually at the ends of the inflorescence axes, on pedicels 1–2 (–3) mm long; hypantho-calyx green, broadly cupuliform, 2–2.5 mm high × 5 mm wide, margin shallowly sinuate; lobes broadly rounded, each with scarious margin regularly incised ± to the base, together forming a ring of 8 whitish, deltoid-acute teeth ca. 1 mm high; corolla in bud sharply apiculate (apiculum ca. 1 mm high); petals white, broadly ovate to rhombiform, 4 × 3 mm, truncate at base above the short claw ca. 0.5 mm long, midnerve impressed on the adaxial surface, prominent on the abaxial surface forming a keel that extends at the apex into a sharp acumen ca. 1 mm long; staminal filaments 4 mm long; anthers dolabriform, 1.25–1.5 × 0.75–1 mm, the connective with thecae positioned at the anterior end, strongly incurved by the dorsal oil-gland; style ca. 7 mm long; epigynous chamber with membranous partitions forming a V-shaped structure beneath each petal and with a low, non-membranous ridge radiating from the base of the style towards each episepalous stamen. Fruits baccate, 1-seeded, green before maturity, subglobose, 5–7 mm in diameter, crowned by the persistent calyx 1.5–2 mm high, thickened and collar-like with the lobes curved inwards partially concealing the epigynous chamber; scarious teeth on calyx margin not persistent or only partially so.

Additional specimens examined (paratypes):— MOZAMBIQUE. Prov. Gaza: M-cel tower, ± 10 km from Bilene on road to Macia , elevation 70 m, 24 July 2005, Burrows 9050 ( BNRH!) ; next to M-cel tower 10 km from Bilene on road to Macia , elevation 67 m, 25°11'31"S, 33°12'36"E, 11 December 2009, Burrows et al. 11512 ( BNRH!, NU!) ; M-cel tower forest, ca. 11 km from Bilene beach to Macia , 25°11'31"S, 33°12'31"E, elevation 61 m, 17 March 2016, Matimele & Tokura 2208 ( BNRH, LMA?, NU!) .

Distribution and habitat: —Known only from the type locality in Gaza Province, southern Mozambique, about 10 km inland from Praia do Bilene ( Fig. 3 ). Small remnant of tall coastal forest occupying the slopes of a low sand hill (ancient dune) at 60–70 m elevation. In March 2016 there were 42 individuals of M. incisilobum counted (according to the collection-label of Matimele & Tokura 2208).

Phenology: —Flowers in late October. Immature fruits in mid-March.

Conservation status: — Memecylon incisilobum is known from a single location and has an extent of occurrence (EOO) and area of occupancy (AOO) of 0.005 km 2 or less, according to Matimele (2016) who has further noted that the species is threatened by forest clearing for subsistence agriculture, wood-cutting for charcoal production, and runaway fires. For these reasons, Matimele (2016) has assessed Memecylon incisilobum (as Memecylon sp. nov.) as Critically Endangered [CR A3cd; B1ab(i, ii, iii, v)+2b(iii); C2a(ii)] following the IUCN Red List Categories and Criteria ( IUCN 2012).

Etymology: —The epithet incisilobum is an adjective referring to the incised calyx-lobes, this being one of the main features distinguishing this species from M. natalense .

Discussion: — Memecylon incisilobum is closely related to another new species, still undescribed, that is known from a single locality in the Kosi Bay Nature Reserve, northeastern KwaZulu-Natal, South Africa. The two populations are separated by an airline distance of ca. 200 km, yet their nrDNA spacer sequences, obtained from the samples Burrows et al. 11512 (BNRH) and Styles 3539 (NH), have 100% identity with respect to each other, seemingly an indication of recent divergence. Molecular phylogenetic analyses suggest that the Gaza and Kosi Bay populations are more closely related to the Mt Mulanje population in southern Malawi (described below as M. nubigenum R.D. Stone & I.G. Mona , sp. nov.) than they are to typical M. natalense sampled further to the south in KwaZulu-Natal ( Stone 2014, Stone et al. 2017). In the present study, we have found that the Gaza and Kosi Bay populations share the features of calyx-lobes with scarious margin and anther connectives yellow in color, which clearly sets them apart from M. natalense in which the calyx-lobes remain subcoriaceous throughout and green (sometimes suffused with dark purple) and the anther connectives are white.

Morphologically, M. incisilobum is clearly distinguished from the Kosi Bay Memecylon by its cymes solitary or rarely geminate (vs cymes solitary or in fascicles of 2–3); longer inflorescence axes (peduncles mostly 5–10 mm not 3–5 mm, secondary axes mostly 3.5–7 mm not 2–3 mm); more numerous flowers (up to 9 flowers per cyme vs flowers mostly 1–3, rarely 4 or 5 per cyme); hypantho-calyx differently shaped (broadly cupuliform vs obconic to cupulopatellate); calyx-lobes with scarious margin ca. 1 mm high and regularly incised ± to the base (vs scarious margin ca. 0.5 mm high and irregularly erose-denticulate or occasionally with one lobe shallowly incised); corolla in bud sharply apiculate with apiculum ca. 1 mm high (vs rounded-apiculate); shorter styles (ca. 7 mm vs 8–10 mm); and fruits with calycinal crown thickened and collar-like with lobes curved inwards (vs calycinal crown not thickened and collar-like, lobes erect). There also seems to be a difference in their respective flowering times (late October for M. incisilobum , early December for the Kosi Bay Memecylon ).

Memecylon incisilobum differs from M. natalense by its elliptic leaf-blades with transverse veins prominent on both surfaces in dried material (vs blades ovate with transverse veins ± obscure especially on the lower surface); cymes borne mostly at the defoliated nodes of older branchlets (vs cymes mostly axillary and at the bracteate nodes alternating with those bearing fully developed leaves), on peduncles mostly 5–10 (–13) mm long and up to 9-flowered (vs peduncles mostly 0.5–5 mm long and 1–4-flowered); hypantho-calyx broadly cupuliform with calyx-lobes scarious and regularly incised ± to the base (vs hypantho-calyx obconic, the margin slightly and obtusely 4-lobed); corolla in bud sharply apiculate (vs rounded); anther connectives yellow (vs white); and fruits with calycinal crown thickened and collar-like with lobes curved inwards (vs calycinal crown not thickened and collar-like, lobes spreading) ( Table 1).

In comparison to M. insulare it has a larger stature (a tree to 7 m vs a shrub to 2 m); larger leaves (mostly 5–7 × 2.5–3.5 cm vs 1.5–4.5 × 0.5–2.7 cm) that are ± broadly and obtusely acuminate at apex (vs leaf apices obtuse to rounded) and have transverse veins faintly visible on both surfaces (vs transverse veins obscure); and somewhat larger flowers (hypantho-calyx 2–2.5 × 5 mm vs 2 × 3.5 mm, petals 4 × 3 mm vs 3.5 × 2.5 mm). However, M. incisilobum and M. insulare are rather similar in their inflorescence dimensions (1–9-flowered vs up to 12-flowered), the acutely apiculate shape of the corolla in bud, and in having petals keeled on the back ( Table 1).

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Figures

FIGURE 1. Memecylon incisilobum. A. Flowering branch. B. Leaf. C. Floral bud. D. Open flower. E. Petal. F. Stamen. G. Fruit. (A–F from Burrows 14765, BNRH; G from Matimele & Tokura 2208, BNRH). Drawing by Sandie Burrows.

FIGURE 2. Memecylon incisilobum. A. Leafy branchlet; B. Trunk showing character of the bark. C. Flower. D. Fruiting branchlet. Photographs in A–C by John Burrows; in D by Hermenegildo Matimele.

FIGURE 3. Distribution of species of Memecylon section Buxifolia in Mozambique and adjacent parts of Malawi and Tanzania: M. incisilobum (black star); M. nubigenum (black triangles); M. rovumense (black circles); M. aenigmaticum (open diamond). Political boundaries are indicated by solid lines, and selected cities by open squares.