Aulostemon Mart.

1. Aulostemon Mart.- Azorín, M.B.Crespo, M.Pinter & Wetschnig

in Phytotaxa 321(3): 288 (2017) ≡ Drimia sect. Aulostemon (Mart.-Azorín, M.B.Crespo, M.Pinter & Wetschnig) J.C.Manning & Goldblatt in Strelitzia 40: 123 (2018) (Fig. 7). Typus generis:— Aulostemon mzimvubuensis (Van Jaarsv.) Mart. -Azorín, M.B.Crespo, M.Pinter & Wetschnig (holotype) ≡ Drimia mzimvubuensis Van Jaarsv. in Aloe 42: 83 (2005), basionym.

Description:—Bulbous geophyte. Bulb partially epigeal, with thickened, fleshy, semitranslucent, loose, rounded and club-shape scales, with short, flattened stalks, easily proliferating when detached, not producing threadlike structures when broken. Roots thickened and branched. Leaves 1‒4 per bulb, linear, up to 50 cm long, 2‒3 mm in diam., leathery, dark green, subterete, slightly channelled on adaxial side, finely striate with minute hairs. Inflorescence a long and lax raceme up to 20 cm long, with 20‒50 nodding flowers; peduncle 25‒40 cm long; pedicels 14‒20 mm long; peduncle and pedicels long persistent and photosynthetic after seed dispersal lasting from flowering time in spring to autumn. Bracts 3‒5 mm long, lanceolate, acute, lowermost with long basal spur to 8‒9 mm long; bracteoles absent or rarely present and minute. Flowers stellate, nodding, opening in afternoon. Tepals 6, biseriate, free from base, outer tepals lanceolate, 10‒11 × 2.5‒2.8 mm, inner tepals oblong-lanceolate, 9‒10 × 3.0‒ 3.5 mm; adaxial side of tepals white with green macula at base that connect to form green basal perigone ring; abaxial side of tepals white with narrow central and longitudinal green band, perigone also showing green basal ring. Stamens 6; filaments flattened and connate along most of their length to form distinct erect tube of ca. 3.5 mm long around gynoecium, ending in short triangular lobes of ca. 1 mm long; anthers free, basifixed, sagittate, connivent to style, ca. 3 mm long, dehiscing by minute apical pores. Ovary ovoid, trigonous, ca. 2.8 × 1.8 mm, green. Style narrow, erect, ca. 4.5 mm long, straight, mostly included in filament tube and connivent anthers, elongating to overtop anthers after dehiscence of the latter. Stigma small and indistinctly trigonous. Capsule triloculate, loculicidal, 7‒10 × 5.4‒7.5 mm, valves splitting to base. Seeds numerous, flattened, suboblong to ellipsoid, 4.5‒6.0 mm long, with prominent embryo and wide, flat wings, black, with sinuous anticlinal testa cell walls (Martínez-Azorín et al. 2017) (Fig. 7).

Number of species and distribution:— Aulostemon includes a single species restricted to the Eastern Cape Province of South Africa, where it occurs northwest of Port St. Johns in the Mzimvubu (uMzimvubu) River gorge, which is resticted to the Uzambara-Zululand Region (sensu Takhtajan 1986) (Fig. 8). For further information on Aulostemon see Van Jaarsveld & Van Wyk (2005), Martínez-Azorín et al. (2017), and Manning & Goldblatt (2018).

Karyology:—Apparently not studied yet (Goldblatt et al. 2012).

History, diagnostic characters, and taxonomic relationships:— Aulostemon is almost unique in Urgineoideae by having filaments of stamens distinctly connate for most of their length to form a long tube that surrounds the gynoecium above the perigone, only resembling those of Chionodoxa and Scilla vardaria, and a green ring at the base on the adaxial side of tepals. This, together with the anthers dehiscing by apical pores or slits, and the long-lasting photosynthesizing inflorescence and pedicels, make recognition of this genus very easy (Martínez-Azorín et al. 2017). The presence of green basal maculae of tepals is a rare character that has also been used to recognise Mucinaea, a genus in Urgineoideae also easily distinguishable by, among other characters, its purplish-pink tepals bearing a doubleeyed green floral marking at their base, surrounded by a white margin—a unique combination of traits in Urgineoideae (Pinter et al. 2013). Martínez-Azorín et al. (2013a) transferred Drimia mzimvubuensis Van Jaarsv. in Van Jaarsveld & Van Wyk (2005: 83) to Sagittanthera, based on the similar general flower morphology and distribution. Later, Martínez-Azorín et al. (2017) have shown morphological differences supporting the independent generic status of Sagittanthera and Aulostemon. This conclusion is also supported by phylogenetic analyses (Martínez-Azorín et al. 2023a) showing that Aulostemon is related to Rhadamanthopsis — a genus showing very different flower morphology with campanulate nodding flowers, connate tepals, and free filaments (in part adnate to the perigone tube) and anthers.

Accepted species:—

Aulostemon mzimvubuensis (Van Jaarsv.) Mart.-Azorín, M.B.Crespo, M.Pinter & Wetschnig in Phytotaxa 321(3): 288 (2017) ≡ Drimia mzimvubuensis Van Jaarsv. in Aloe 42(4): 83 (2005), basionym ≡ Sagittanthera mzimvubuensis (Van Jaarsv.) Mart.-Azorín, M.B.Crespo, A.P.Dold & Van Jaarsv. in Phytotaxa 98(2): 51 (2013) (Figs 1.1, 7). Type:— SOUTH AFRICA. Eastern Cape Province. Port St. Johns (3129): lower Mzimvubu River, south facing shale cliffs near Lutengela, (–CB), Van Jaarsveld, Xaba, Harrower & Zwide 58 (PRE holo.).