Aloe uigensis Gideon F.Sm. & T.Lautenschl., 2021

Smith, Gideon F. & Lautenschläger, Thea, 2021, Aloe uigensis (Asphodelaceae subfam. Alooideae), a new species from northwestern Angola, Phytotaxa 521 (3), pp. 227-231 : 228-230

Aloe uigensis Gideon F.Sm. & T.Lautenschl. , sp. nov. ( Figs 1 and 2E ).

Type:— ANGOLA. Uíge Province —07014 (Ambuila): municipality of Ambuila, near the village of Pambu (–DA), on limestone rocks, 23 November 2015, Thea Lautenschläger TL2015 _11_63 (holotype DR DR 067649 [available online at https://www.jacq.org/detail. php? ID =1743069], isotype B B101154436 [available online at http://herbarium.bgbm.org/object/ B101154436 ]) .

Diagnosis:— Aloe uigensis does not appear to have obvious close relatives in Angola. Plants of this species differ from other Angolan aloes by being tall-growing, single-stemmed, and bearing narrowly elongated, acuminate racemes. Although A. andongensis Baker (1878: 263) and A. varimaculata McCoy (2016: 279) also bear somewhat narrowly elongated, acuminate racemes, both species are shrubby rather than single-stemmed, smaller-growing than A. uigensis , and both occur much further south in Angola. Furthermore, A. andongensis has branched racemes, while those of A. uigensis are unbranched. In contrast, the widespread, single-stemmed A. littoralis Baker (1878: 263) has broad, boat-shaped leaves, very large, robust rosettes perched at the top of sturdy stems, and plants bear multi-branched panicles, unlike A. uigensis that is a more dainty plant, has narrower leaves, and bears unbranched racemes.

Description:—Perennial, medium-sized, herbaceous, single-stemmed succulent, ± 1 m tall when not in flower. Roots terete, cylindrical. Stem 0.6 m long, erect to variously leaning, ± 20–35 mm in diam. Leaves to 45 cm long, 5 cm broad at base, bright verdant green, concolorous, adaxially unspotted, abaxially irregularly white-spotted mainly in the apical half, crowded towards stem apex, persistent for a long time, narrowly attenuate, basally sheathing, erect to spreading when young, becoming decurved with age; margins with short, sharp teeth, straight or curved towards leaf tips or leaf base; teeth 2–3 mm long, ± evenly spaced, ivory-coloured with very tip reddish brown, gradually decreasing in size towards apex; leaf exudate yellowish when fresh and dry. Inflorescence an unbranched, laxly-flowered raceme, 0.55 m long, narrowly elongated, acuminate; a rosette producing a single raceme. Peduncle basally plano-convex in crosssection, round in cross-section above, 0.34 m long, 10 mm broad at base, greyish brown, covered in a powdery bloom, sparsely sterile bracteate; sterile bracts 15–20 mm long, 10–15 mm broad at base, creamy brown, with ± 11 orangebrown nerves, tapering to blunt, harmless tip. Raceme laxly flowered with ± 30 flowers, flowering portion 0.19 m long, up to 70 mm in diam. at level of open flowers; buds erect to spreading, lowest open flowers pendent. Floral bracts creamy brown, papery, amplexicaul around pedicel, apices attenuate, with 10–15 orange-brown nerves, 13–15 mm long. Pedicels light green, 12–14 mm long when flowers open, remaining the same length in fruit. Flowers self-sterile, 20–25 mm long, 6–7 mm in diam. at ovary, orange to pale reddish, tip extremity yellowish, unscented, nectariferous, pencil-shaped, cylindric-trigonous, tips slightly spreading to slightly recurved, very slightly widest in middle, not indented above ovary, slightly narrowing towards mouth, erect post-anthesis; perianth segments in two whorls, outer segments free for ± 20 mm; buds same colour as open flowers but strongly green-tipped, exserted beyond bracts; stamens with white, filiform-flattened filaments, exserted to 5 mm; ovary 6.0 × 2.5 mm, light green; style exserted to 1 mm. Fruit and Seed not seen. Chromosome number: unknown.

Etymology:— Aloe uigensis is named for the province of Uíge in northern Angola, from where the type specimen was collected.

Geographical distribution range and habitat:— At present A. uigensis is known only from the type locality in the municipality of Ambuila , near the village of Pambu in northwestern Angola, where plants grow in crevices in rocks on limestone inselbergs ( Fig. 2 ). The area is part of the Regional Transition Zone between the Guineo-Congolian and the Zambezian Regions ( White 1983: 170) .

Species that grow in association with A. uigensis include Obetia carruthersiana ( Hiern 1900: 987) Rendle (1917: 245) [ Urticaceae ], Euphorbia conspicua Brown (1912: 600) [ Euphorbiaceae ] (but see Figueiredo & Smith 2018, 2020 on the nomenclature of E. conspicua ), and Cussonia angolensis ( Seemann 1865: 34) Hiern (1877: 32) [ Araliaceae ].

Discussion:—As far as we are aware, of the Aloe species recently described from Angola, i.e., following the publication of Klopper et al. (2008, 2009, 2010), only one, A. mocamedensis Van Jaarsveld (2012: 173) , is generally single-stemmed, but this is a desert species that is endemic to southwestern Angola and its stem is often creeping. In contrast, A. uigensis is from a more mesic environment in northwestern Angola and it grows erect. Aloe andongensis and A. varimaculata , both also from further south in Angola, are smaller-growing, shrubby species.

Geographically, the very widespread and unbranched A. littoralis , which can reach a height of 2(–4) m, has been recorded from the provinces of Luanda, Bengo, and Cuanza Norte ( Reynolds 1966: 319). Bengo and Cuanza Norte abut Uíge in the south, with, as far as is known, A. littoralis therefore being the aloe that occurs closest to the type locality of A. uigensis . However, A. littoralis has broad, boat-shaped leaves, very large, robust rosettes perched at the top of sturdy stems, and plants bear multi-branched panicles, unlike A. uigensis that is a more dainty plant, has narrower leaves, and bears unbranched inflorescences.

As far as is known, aloe expert Gilbert W. Reynolds, who visited Angola in June and July 1959 and described six new species from the country ( Klopper et al. 2009: 21), did not collect in Uíge province ( Reynolds 1960).

Figures

FIGURE 1. Aloe uigensis. A. Stem with some of the dry leaves removed. B. Basal portions of leaves. C. Teeth along leaf margin. D. Raceme. E. Close-up of flower. F. Apical portion of flower showing spreading to slightly recurved tips of perianth segments and exserted anthers. G. Close-up of a sterile bract showing longitudinally-arranged, orange-brown nerves. H. Point of attachment of anther to filament. I. Apical view of ovary. J. Lateral view of ovary. Scale bar = 1 mm. Photographs: Thea Lautenschläger.

FIGURE 2. Distribution map and habitat of Aloe uigensis. A. Location of Angola in Africa. B. Location of Uíge province in Angola. C. Map of Uíge province with vegetation zones and location of type specimen (black dot) indicated. Vegetation zones follow Barbosa (1970: 92–95). The type locality of A. uigensis falls in “Tipo de vegetação N.o 9, Mosaico de savanna zambeziaca e floresta cafeeira”. D. Limestone inselberg, a typical habitat of A. uigensis. E. Aloe uigensis growing socially with Obetia carruthersiana. Photographs: Thea Lautenschläger.