Cladoceras rovumense I.Darbysh., J.E.Burrows & Q.Luke, 2022

Darbyshire, Iain, Burrows, John E., Luke, Quentin & Langa, Clayton, 2022, Cladoceras rovumense sp. nov. (Gentianales-Rubiaceae), a new species from southeast Tanzania and northeast Mozambique, European Journal of Taxonomy 833, pp. 46-59 : 50-54

Cladoceras rovumense I.Darbysh., J.E.Burrows & Q.Luke sp. nov.

urn:lsid:ipni.org:names:77302733-1

Figs 1–3

Tarenna sp. 53 sensu Degreef, Opera Botanica Belgica 14: 143 ( Degreef 2006); Timberlake et al., Plant Ecology and Evolution 144: 131 ( Timberlake et al. 2011); Burrows et al., Trees and Shrubs Mozambique ( Burrows et al. 2018); Darbyshire et al., Plant Ecology and Evolution 153: 441 ( Darbyshire et al. 2020).

Diagnosis

Cladoceras rovumense sp. nov. resembles C. subcapitatum in floral and fruit morphology, but differs most markedly in (a) being a free-standing tree or shrub, lacking modified spinose lateral branches (vs a scandent shrub with some lateral branches modified to form ± recurved spines to aid climbing in C. subcapitatum ); (b) the leaves being obovate or obovate-elliptic, larger, up to 17.5 × 10.5 cm, with surfaces pubescent particularly on the veins beneath and midrib above, becoming scabridulous at maturity (vs leaves elliptic to oblong-oblanceolate, smaller, up to 12 × 4.8 cm, glabrous); (c) the inflorescences being borne on leafless lateral branches (vs inflorescence-bearing branches with one or more pairs of leaves at least in flower, sometimes caducous at fruiting); (d) the inflorescence being dense, capitate and with 20+ flowers (vs less dense and usually with clear branching, 9–15-flowered); (e) the calyx lobes being rounded to broadly and convexly triangular, with an irregular, sometimes toothed margin (vs calyx lobes acute-triangular to -lanceolate); and (f) the style and stigma together measuring 17–19 mm long (vs 8–10 mm long in C. subcapitatum ); see Table 1 .

Etymology

The epithet denotes that this species is endemic to the proposed Rovuma CoE in coastal southern Tanzania and northern Mozambique.

Type MOZAMBIQUE • Cabo Delgado Prov., Quiterajo, Pt. 463; 11.7676° S, 40.3743° E; alt. 115 m; 24 Nov. 2009; Q. Luke 13883; holotype: K [ K000787442 ]; isotypes: EA, LMA, MO, P.

Paratypes MOZAMBIQUE • Cabo Delgado Prov., Mueda Plateau; 11°20ʹ S, 39°26ʹ E; alt. 760 m; 14 Dec. 2003; [W.R.] Q. Luke, O. Kibure & E. Nacamo 10116; EA, K, LMA, MO, UPS • Cabo Delgado Prov., Namacubi Forest (the Banana) , west of Quiterajo; 11°45ʹ55ʺ S, 40°23ʹ45ʺ E; alt. 90 m; 25 Nov. 2008; J.E. & S.M. Burrows 10748; BNRH, K, LMA.

TANZANIA • Lindi Region, Rondo Plateau, Rondo Forest Reserve ; 10°07ʹ S, 39°13ʹ E; alt. 750 m; 6 Feb. 1991; S. Bidgood, R. Abdallah & K. Vollesen 1357; K (2 sheets), NHT.

Description

Small, slender deciduous tree or shrub 1.5–7 m tall; young stems ± quadrangular, with papery maroonbrown bark that readily exfoliates in strips or patches, at first puberulous with ± patent hairs to 0.35 mm long but soon glabrescent. Stipules soon caducous, triangular, 3.7–7.5 mm long, with a thickened blackish-brown central portion and with paler, somewhat hyaline margins but these often infolded in dry material, glabrous externally, with long pale hairs internally. Leaves clustered towards ends of main and widely divergent lateral branches, ± immature at flowering, subsessile or on puberulent petiole to 7 mm long; blade of mature leaves obovate or obovate-elliptic, 9–17.5 × 5.8–10.5 cm (l/w ratio 1.55–1.9: 1), base cuneate to somewhat attenuate or some leaves abruptly obtuse at base, apex shortly acuminate or (sub)attenuate, lateral veins 7–11 per side, these and the midrib prominent and often pale beneath, surfaces pubescent with hairs densest and longest on veins beneath and midrib above, conspicuous when young, becoming more sparsely hairy with maturity, the blade then scabridulous; minute pocketdomatia present in axils of lateral veins beneath but inconspicuous. Inflorescences terminating leafless lateral branches 11–28.5 cm long, flowers 20 or more, sessile, crowded in capitate corymbs with highly reduced and thickened branches; bracts subtending the main inflorescence branches maroon at least at apex, triangular with a slender apiculum, 3.2–4.5 × 3–4 mm, those subtending the flower clusters smaller, 1–2.5 mm long. Calyx tube (hypanthium) 1.9–2.7 mm long; calyx lobes pink- to maroon-tinged, rounded to broadly and convexly triangular, ± 1 mm long, with an irregular, sometimes toothed margin, glabrous or margins sparsely ciliate. Corolla white except for yellowish-green tube and central portion of lobes externally, glabrous externally; tube narrowly cylindrical, (30–)38–42 × 1.5–2 mm, pilose with long wispy hairs internally mainly in distal half; lobes oblong-elliptic, 5–9 × 3.7–4.2 mm. Stamens with anthers subsessile, held at corolla mouth, 2.6–3 mm long. Ovary bilocular, placentae affixed centrally on septum; style and stigma together 17–19 mm long, glabrous, stigma ± linear, included within corolla tube. Fruit pale green, globose-obovoid, 6–8 mm in diameter, endocarp thin, glabrous, calyx persistent, usually 6–8 seeds per fruit (as few as 2 seeds per fruit reported by Degreef 2006); seeds orange-brown, 4–5 mm in diameter, hemispheric with a slightly angular lower side and a deep circular hilar excavation ca 1.5 mm in diameter, testa smooth and glossy.

Distribution and habitat

Restricted to the proposed Rovuma CoE, known from the Rondo Plateau of Southeast Tanzania and the Mueda Plateau and Namacubi Forest (Quiterajo) in northeast Mozambique ( Fig. 3 ). Occurs in deciduous and semi-evergreen coastal and lowland dry forest and thicket on sandy soils, including areas of secondary woodland/thicket, at 90–760 m altitude. At Quiterajo, it was recorded from Guibourtia schliebenii (Harms) J.Léonard dominated dry forest with species of Memecylon L., Warneckea Gilg and Strynchnos L. common in the understorey (J.E. & S.M. Burrows 10748). The type specimen from the same site was found growing in close proximity to a number of rare and globally threatened species, i.e., Xylopia tenuipetala D.M.Johnson & Goyder (Q. Luke 13884), Vismianthus punctatus Mildbr. (Q. Luke 13885), Vismia pauciflora Milne-Redh. (Q. Luke 13886A) and Warneckea cordiformis R.D.Stone (Q. Luke 13887). On the Rondo Plateau, it was noted from within forest of Milicia excelsa (Welw.) C.C.Berg , Dialium L., Albizia Durazz. , and Pteleopsis Engl. (= Terminalia L. according to some authorities).

Conservation status

This species is known from three locations and has an extent of occurrence of 6601 km 2 and a calculated area of occupancy of 16 km 2. At Mueda Plateau, there has been an estimated loss of dense woodland and dry forest vegetation cover of over 96%, whilst in the Rio Messalo-Quiterajo area this figure is 71.2% ( Timberlake et al. 2011). On the Rondo Plateau in Tanzania, 2755 ha of natural forest were cleared during the Rondo Forest Programme in 1952–1978 and replaced by commercial plantation of exotic tree species. Some clearance of natural forest for subsistence agriculture and for fuelwood collection is an ongoing threat at this site ( Clarke 2001). However, a sizeable area of forest remains on the western slopes of the plateau, some of which has regenerated since the cessation of forestry. The gazetting of this site as a Nature Forest Reserve in 2016 may hopefully result in increased protection for the biodiversity there ( Wabuyele et al. 2020). With only three locations and a continuing decline in the extent and quality of habitat at the majority of these sites, this species is provisionally assessed as Endangered – EN B2ab(iii).

Figures

Fig. 1. Cladoceras rovumense I.Darbysh., J.E.Burrows & Q.Luke sp. nov. A. Habit, fruiting shoot. B. Habit, flowering shoot. C. Stipule, external face. D. Hairs revealed beneath fallen stipule. E. Portion of flowering stem showing indumentum. F. Leaf, adaxial indumentum. G. Leaf, abaxial indumentum. H. Dissected corolla with androecium. I. Style and stigma. J. Longitudinal section of ovary. K. Mature fruit. L. Fruit, partially dissected to reveal seeds. M. Seed in two views. A, E–G, K–M from S. Bidgood et al. 1357; B, H–I from Q. Luke 13883; C–D, J from Q. Luke et al. 10116. Drawn by Andrew Brown.

Fig. 2.Species of Cladoceras Bremek. in the field. A–B. Cladoceras rovumense I.Darbysh., J.E.Burrows & Q.Luke sp. nov. (photos: A. Q. Luke; B. P.A. Luke, Mozambique). C–D. Cladoceras subcapitatum (K.Schum. & K.Krause) Bremek. (photos: W.R.Q. Luke, Base Titanium nursery, Kwale County, Kenya).

Fig. 3. Distribution of Cladoceras rovumense I.Darbysh., J.E.Burrows & Q.Luke sp. nov.