Memecylon rovumense 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 : 160-163

Memecylon rovumense R.D. Stone & I.G. Mona , sp. nov. ( Fig. 5 )

Type:— TANZANIA. Lindi Region: Lindi District, Chitoa Forest Reserve, elevation 240–420 m, 9°58’S, 39°27’E, 18 June 1995, Clarke 56 (holotype K!).

Evergreen shrub or understory tree up to 6 m tall; young branchlets quadrangular (subquadrangular below the “aphyllous” nodes); nodes thickened; internodes between normal leafy nodes (1–) 2.5–6.5 (–11) cm long; bracts of the “aphyllous” (i.e., inflorescence-bearing) nodes lanceolate, ca. 3 mm long, rapidly deciduous. Leaves coriaceous, on petioles 1–3 (–4) mm long; blades elliptic to ± ovate or obovate, (2.5–) 3.5–5.5 (–7) × (1.3–) 1.8–3.3 (–4) cm, cuneate at base, ± broadly and obtusely acuminate at apex, the acumen (1–) 2–4 (–5.5) mm long or sometimes indistinct with the leaf apex then rounded and obtuse; midnerve clearly visible, impressed on the upper surface, ± prominent on the lower (especially toward the leaf base); intramarginal nerves faintly visible; transverse veins 3–5 pairs, oriented at an oblique angle relative to the midnerve, faintly visible in dried material. Cymes 1–3 (–4)-flowered, solitary to geminate or in fascicles of 2 (–3), borne 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; peduncles 1.5–2 mm long; secondary axes ± absent, the flowers thus directly subumbellate; bracts ca. 2 mm long, ± lanceolate, narrowed to the base, rapidly deciduous. Flowers in bud on very short pedicels, corolla rounded-apiculate; fully developed and open flowers not seen. Fruits baccate, 1-seeded, green before maturity, broadly pyriform, 18 × 14 mm, conspicuously verrucose-wrinkled, lacking a calycinal crown but with lobes persistent, broadly deltate and ca. 1 mm long, curved inwards partially concealing the epigynous chamber.

Additional specimens examined (paratypes):— MOZAMBIQUE: Prov. Cabo Delgado: Namacubi (Banana) Forest west of Quiterajo , elevation 90 m, 11°45'55"S, 40°23'45"E, 25 November 2008, Burrows 10766 ( BNRH!, K!) ; Quiterajo , elevation 110 m, 11°45'48.24"S, 40°21'47.16"E, 24 November 2009, Luke 13891 ( EA!, K!, LMA, P) ; Namacubi Forest near Quiterajo , elevation 90 m, 11°45'23"S, 40°24'00"E, 08 September 2014, Timberlake & Massingue s.n. ( NU!) . TANZANIA. Lindi Region: Chitoa Forest , elevation 415 m, 05 December 2001, Mbago et al. 2266 ( DSM, K!) ; Kilwa District , ca. 1 km W of Miteja soccer pitch, elevation 50 m, 08°16'14"S, 39°13'36"E, 03 August 2003, Kayombo et al. 4431 ( CAS!, MO) ; Ngarama North Forest Reserve , elevation 420 m, 09°24'S, 39°19'E, 26 November 2003, Luke & Kibure 9741 ( CAS!, EA!, MO) .

Distribution and habitat: —Known from three locations in southern Tanzania (Lindi Region) and one location in northern Mozambique (Namacubi Forest near Quiterajo, Cabo Delgado Province) ( Fig. 3 ). Coastal dry forest at elevations of 50– 420 m.

Phenology: —Floral buds in late November; fruits in June.

Conservation status: — Memecylon rovumense is known from four locations including three in southeastern Tanzania (Lindi Region) and one in northern Mozambique (Cabo Delgado Province). It has an EOO of ca. 8,400 km 2 and an AOO of ca. 24 km 2 (assuming a 4 km 2 grid-cell size).

The coastal forests of East Africa are small and highly fragmented, most of them being less than 50 km 2 in size ( Burgess et al. 2000). They are thought to be remnants of a more extensive forest cover that existed prior to the spread of dry climate in this region beginning ca. 16 Myr ago ( Jacobs 2004); however, recent disturbance by human activities (especially increased fire frequency) has also contributed to the reduction and fragmentation of these forests ( Burgess et al. 1998).

In Tanzania, M. rovumense currently receives an uncertain level of protection, in spite of the fact that two of the three known locations lie within gazetted forest reserves. This is because the management budgets and staffing levels are extremely low ( Burgess et al. 2012). The Chitoa Forest Reserve, which includes the type locality, is ca. 45 km west of the coastal town of Lindi. It is a small reserve (7.7 km 2) with only 1.8 km 2 designated as “protective” forest and the remaining 5.9 km 2 as “production” forest intended for sustainable use ( Clarke 1995, Burgess et al. 2012). In total, the Chitoa Plateau and nearby Litipo Forest Reserve contain an estimated 8 km 2 of mixed dry forest ( Prins & Clarke 2007). The Chitoa Forest Reserve is located 3 km away from the nearest villages and is only accessible by footpath; this suggests that threats to the forest may be limited, although Clarke (1995) noted some wood cutting of poles by local people and the possibility of uncontrolled bushfires. About 65 km further to the north, the Ngarama North Forest Reserve is larger (ca. 45 km 2) with 15 km 2 designated as “protective” forest and the remainder as “production” ( Burgess et al. 2012). The reserve is situated on the Ruwawa Plateau largely covered by “scrub forest” over coral rag limestone, but with 13 km 2 of mixed dry forest and legume-dominated dry forest ( Prins & Clarke 2007). Threats are minimal because of low human population density in the area, although some timber poaching has been seen ( Prins & Clarke 2007). The remaining coastal forests of the Lindi Region (SE Tanzania) are also threatened by recent improvements in road infrastructure, which are opening up previously remote and relatively inaccessible areas for logging and charcoal production ( Prins & Clarke 2007, Burgess et al. 2012).

In Mozambique, the only known location of M. rovumense is not in a protected area. Ongoing threats in the Namacubi Forest include continued clearing for subsistence agriculture, cutting of poles, uncontrolled fires, and possible road construction for oil-and-gas development which would increase access to and clearing of the forest ( Timberlake et al. 2011, Cheek & Darbyshire 2014).

Memecylon rovumense is thus provisionally assessed as Endangered [EN B1ab(iii)+B2ab(iii)] according to the IUCN Red List Categories and Criteria ( IUCN 2012).

Etymology:— The epithet rovumense is an adjective used to indicate geographical origin, i.e., to emphasize that the new species is an endemic of the Rovuma region of northern Mozambique and southeastern Tanzania. The region itself gets its name from the Rovuma River which forms the border between these two countries.

Discussion: — Memecylon rovumense has been previously confused with M. natalense , but DNA evidence suggests it may have originated through hybridization between a lineage close to the Kenyan M. fragrans A. Fernandes & R. Fernandes (1960: 87) and another, as-yet unidentified Mozambican lineage close to M. torrei (Stone et al. 2017) . Its fruits are quite distinctive in being relatively large, yellow-green and warty-roughened on the exterior, appearing much like miniature avocados, seen in the collection Clarke 56 (K).

It differs from South African M. natalense by its more thickly coriaceous leaves that are rounded and obtuse to ± broadly obtuse-acuminate at the apex (vs thinly coriaceous with acumen acute), by its 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), and by its larger, broadly pyriform and conspicuously verrucose-wrinkled fruits lacking a persistent calycinal crown (vs fruits up to 10 mm in diameter, ellipsoid to subglobose with smooth exterior and calycinal crown conspicuous) ( Table 1).

In comparison to the Kenyan M. fragrans it has broader, differently shaped leaves (mostly 3.3–5.5 × 1.7–3.3 cm and ± elliptic vs 2–5.5 × 1.0– 2.4 cm and ± ovate), and the cymes are 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). The fruits of M. fragrans are also smaller and differently shaped (ovate to elliptic, 8–9.5 × 6–7 mm with exterior only slightly roughened and calycinal crown conspicuous).

In comparison to the Mozambican M. torrei it has somewhat smaller leaves (mostly 3.3–5.5 × 1.7–3.3 cm vs 4–7 × 2–4 cm), and the lower leaf surface is pale green (vs vivid yellowish green) ( Table 1). The fruits of M. torrei are similarly large (ca. 18 × 14 mm) and also with exterior warty-roughened, seen in the collection Goyder et al. 6107 (P).

Figures

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.

FIGURE 5. Memecylon rovumense. A. Fruiting branch. B. Leaf. C. Fruit. (A–C from Clarke 56, K). Drawing by Sandie Burrows.