Lijndenia udzungwarum (Melastomataceae–Olisbeoideae): a new, endemic species from the Udzungwa Mountains of southern Tanzania

Lijndenia udzungwarum R.D. Stone & Q. Luke, a shrub or small tree of Tanzania’s Udzungwa Mountains, is described and illustrated. The placement of the new species in Lijndenia is indicated by its trinervate, papillose-muricate leaves and persistent bracteoles partially fused to form a cupule immediately subtending each flower. The cordate leaves of L. udzungwarum are unique in the genus. From the East African L. brenanii (A. Fern. & R. Fern.) Jacq.-Fél. and L. procteri (A. Fern. & R. Fern.) Borhidi, the new species is further distinguished by its capitellate inflorescences on long, filiform, axillary peduncles, resembling those of the Sri Lankan L. capitellata (Arn.) K. Bremer. Despite its local endemism, L. udzungwarum has been assessed as ‘Least Concern’ according to IUCN criteria, although this assessment is dependent on the continued safeguarding of the Udzungwa Mountains National Park. An identification key is provided for the three currently recognized Tanzanian species of Lijndenia.

Here we describe a distinctive new Lijndenia from the Udzungwa Mountains of southern Tanzania. This species was first collected in the early 1980s and cited by Lovett et al. (1988: 882) as "Memecylon sp. nov.," but clearly belongs in Lijndenia due to its trinervate, papillose-muricate leaves and persistent, cupulate bracteoles subtending individual flowers. The Udzungwas are part of the Eastern Arc Mountains of Tanzania and Kenya, which have been noted for their high degree of floristic endemism (Rodgers & Homewood 1982a, Iversen 1991, Lovett 1993, Myers et al. 2000, Burgess et al. 2007). Evergreen shrub or small tree 2-3 m high; internodes (0.6-) 1.9-3.3 (-3.8) cm long; young branchlets terete in cross section. Leaves thinly coriaceous, dark green above, somewhat paler below, granular on both surfaces in dried material; petioles c. 1 mm long (rarely obsolete or up to 2 mm); blades ovate, (2.4-) 3.2-5.2 (-5.9) cm long, (0.9-) 1.8-2.8 (-3.2) cm long, rounded at base and broadly cordate, acuminate at apex; acumen c. 1 cm long, obtuse; midnerve impressed on the upper surface, prominent on the lower but becoming progressively narrower toward the leaf apex; lateral nerves much thinner than the midnerve, those of the principal pair curvilinear in the basal half of the blade but becoming weak and intramarginal in the apical half; secondary pair of lateral nerves faintly visible in the basal portion of the blade, intramarginal; transverse veins ± obscure. Inflorescences condensed to 3-flowered heads 5-8 mm in diameter, borne on filiform peduncles 10-20 (-27) mm long in the leaf axils; paired bracts at base of head distinct, ovate-lanceolate, c. 1 mm long; bracteoles suborbicular, cucullate, fused in pairs to form a cupule immediately subtending each of the flowers; pedicels 0; hypantho-calyx obconic, 2 mm long × 2.5 mm wide, the lobes broadly triangular, 0.5 mm long, obtuse-rounded to acute; corolla well exposed in bud, the petals white, broadly ovate-deltate, 2 mm long × 1.5 mm wide, rounded and abruptly acute at apex, truncate at base above the claw 0.5 mm long; anthers c. 1 mm long, ± keeled dorsally and lacking an oil-gland, the pollen sacs fronto-ventral; style 3.5 mm long; top of ovary smooth (interstaminal partitions absent). Berries blue-purple, globose, c. 7 mm in diameter, lacking a persistent calycinal crown.

Lijndenia udzungwarum
Additional specimens examined ( Distribution and habitat:-Lijndenia udzungwarum is endemic to the northern part of the Udzungwa Mountains in southern Tanzania (Fig. 2). According to data provided on specimen labels, the habitat of this species is in montane forest at 1350-1700 m elevation.
Of the five collections cited for L. udzungwarum, four are from within the boundaries of the Udzungwa Mountains National Park. This protected area, gazetted in 1992, covers almost 2000 km 2 in the northern Udzungwas and encompasses all of the Mwanihana forest as well as large parts of the Luhombero and Matundu forests.
Three of the collections cited are from the Mwanihana forest, situated along the steep, east-facing escarpment of the northern Udzungwas. This area of approx. 180 km 2 , first gazetted as a Forest Reserve in 1958, includes an estimated 59 km 2 of forest spanning a wide elevational range (from 300 to 2080 m) and subdivided into lowland, transitional (submontane), montane and upper montane forest types (Rodgers & Homewood 1982b, Lovett et al. 1988, Lovett & Pócs 1993a. The label of the type collection (Thomas 3773) clearly states the locality as being in the Mwanihana forest at 1400−1700 m elevation, but the geographic coordinates given (lat. 7°50'S, long. 36°55'E) are incorrect as they would place it at c. 290 m elevation in the Msolwa River valley, east of the Mikumi−Ifakara road. In the Tropicos (2015) specimens database, the coordinates of Thomas 3773 have been revised to lat. 7°47'S, long. 36°52'E.
The fourth collection of L. udzungwarum (i.e. Luke et al. 6700) is from the Luhombero massif, a remote highland plateau that includes the highest peak in the Udzungwas (elev. 2576 m). This area was previously included in the West Kilombero Scarp Forest Reserve, first gazetted in 1957 and comprising 1953 km 2 until the northern portion (910 km 2 including Luhombero) was excised into the Udzungwa Mountains National Park. Vegetation in the area has been generally described as "moist and dry montane and upper montane forest with extensive areas of bamboo and upland grassland with forest patches" (Lovett & Pócs 1993b). The area of natural forest was reported by Rodgers & Homewood (1982b) as 25 km 2 , but this would seem to be an underestimate. The fifth collection of L. udzungwarum (i.e. Price & Mhoro WK329) is from the Nyumbanitu forest, situated in the remaining part of the West Kilombero Scarp Forest Reserve (area 1043 km 2 ) bordering the Udzungwa Mountains National Park on the west. The total forest cover within this reserve is reportedly 305 km 2 , of which 135 km 2 is found at elevations of 1040−2480 m (Frontier Tanzania 2001). Additional localities for L. udzungwarum may yet be found in the Ndundulu and Ukami forests, representing the other two large fragments of montane forest in the reserve.
Phenology:-Flowers in late September to early October. Fruits in October. Conservation status:-Despite the evident restriction of L. udzungwarum to three fragments of montane forest in the northern Udzungwas, the IUCN (2013) has assessed it (as Lijndenia sp. nov.) as being of "Least Concern," citing an absence of documented or observed threats. It was noted however that this assessment is contingent on the continued effectiveness of conservation measures (safeguarding of the Udzungwa Mountains National Park). No new status is proposed in the present work, i.e. the IUCN (2013) assessment of "Least Concern" for L. udzungwarum is confirmed.
Etymology:-The species epithet udzungwarum is a feminine, plural noun (Declension I) in the genitive case. It is used to indicate geographical origin, i.e. to emphasize that the new species is a local endemic of Tanzania's Udzungwa Mountains. Discussion:-From its congeners, L. udzungwarum is immediately distinguished by its cordate leaves (vs. leafbases cuneate to attenuate or rounded in other Lijndenia spp.). The new species further differs from the East African L. brenanii and L. procteri by its 3-flowered, capitellate inflorescences borne on slender peduncles 10-20 (-27) mm long (vs. inflorescences with up to 11 or more distinctly pedicellate flowers borne on thicker, quadrangular peduncles to 11 mm long and with secondary inflorescence axes to 9 mm long). The inflorescence features of L. udzungwarum are most similar to those of the Sri Lankan species, L. capitellata (Arnott 1836: 17) K. Bremer (1982: 123), although this would seem to represent a case of morphological convergence as these two species are not believed to be sisters in a phylogenetic sense or even very closely related.
When L. brenanii and L. procteri were first described under Memecylon sensu lato (Fernandes & Fernandes 1960), each species was known from a single collection, the former from Sangarawe in Tanzania's East Usambara Mountains (Greenway 3680, holotype EA!, isotype K!, fragment P!), the latter from the Shagayu forest in the West Usambaras (Procter 208, holotype EA!, isotypes K!, TFD!). In his key to the species of Memecylon sensu lato for the Flora of Tropical East Africa, Wickens (1975) contrasted the characters of the inflorescence between these two species (i.e. inflorescence compound in L. brenanii vs. simple in L. procteri), but the original diagnoses (Fernandes & Fernandes 1960) also noted differences in habit and leaf size, i.e. L. brenanii a tree to 18 m high with larger leaves to 7.5 cm long × 4 cm wide, vs. L. procteri a shrub to 1.2 m high with smaller leaves to 4.5 cm long × 3 cm wide. Wickens (1975) has suggested that L. procteri might only be a shrubby form of L. brenanii, but this does not seem to be the case as the two taxa occupy distinct geographic ranges and are diagnosably different (see below for a key to the currently recognized Tanzanian species of Lijndenia).
Lijndenia brenanii is evidently an extremely rare species that has been recollected only twice in the Kwamkoro forest near the type locality (Mgaza 437, EA!, K!, TFD!; Ruffo & Mmari 2213, TFD!). In January 2002, the first author could not relocate L. brenanii in spite of several days searching in the East Usambaras, although in the Shume forest (West Usambaras) he did succeed in finding a new Lijndenia population currently determined as L. aff. brenanii (Stone et al. 2438 Stone, unpublished data). Additional collections and further study are needed to discover any morphological differences that might be used to diagnose the southern populations in comparison with typical L. brenanii or L. procteri, and also to determine if the larger-leaved and smaller-leaved plants all belong to the same species. There is an indication that the larger-leaved plants in the Udzungwas are found in the understory of submontane or montane forest (700−1800 m elevation) while the smaller-leaved plants occupy ridgetop sites at 1750−1900 m.
Memecylon cogniauxii Gilg (1898: 44) is another Eastern Arc endemic that superficially resembles L. udzungwarum in having cordate leaves and axillary inflorescences on long slender peduncles. However, M. cogniauxii has apparently uninervate (not trinervate) leaves and clearly belongs in Memecylon sensu stricto (see Stone 2014). Furthermore, M. cogniauxii is known only from the East Usambara, West Usambara, South Pare, Nguru, and Uluguru mountains; it is not known to occur in or near the Udzungwas.

Key to the species of Lijndenia in Tanzania
The identification key provided below includes the new species L. udzungwarum described in the present work, as well as the two other currently recognized Tanzanian species of Lijndenia. In the Flora of Tropical East Africa (Wickens 1975), the latter two species were treated in Memecylon sensu lato (see Introduction). Plants resembling L. brenanii and L. procteri from southern Tanzania (including the Udzungwa Mountains) are not yet fully described (see Discussion), so they are not included in this key.