Aulostemon Mart.

Martínez-Azorín, Mario, Crespo, Manuel B., Pinter, Michael & Wetschnig, Wolfgang, 2017, Aulostemon (Asparagaceae, Scilloideae), a new genus from South Africa, Phytotaxa 321 (3), pp. 287-293 : 288-290

Aulostemon Mart. -Azorín, M.B.Crespo, M.Pinter & Wetschnig gen. nov. ( Fig. 1 )

Similar to Sagittanthera , but differing by the connation of the filaments of the stamens that are as long as or slightly longer than the anthers and form a distinct tube that surrounds the gynoecium (not much shorter than the anthers and free in the former); the free anthers (not connate at least along the distal half); the adaxial side of tepals exhibiting basal green maculae that connect to form a basal green ring (not completely white); and the absence of bracteoles.

Typus generis: — Aulostemon mzimvubuensis (Van Jaarsv.) Mart. -Azorín, M.B.Crespo, M.Pinter & Wetschnig comb. nov. (holotype).

Basionym:— Drimia mzimvubuensis Van Jaarsv. in Van Jaarsveld & Van Wyk (2005: 83) ≡ Sagittanthera mzimvubuensis (Van Jaarsv.) Martínez-Azorín et al. (2013b: 51) . Type:— SOUTH AFRICA. Eastern Cape Province. Port St. Johns (3129CB), lower Mzimvubu River, south facing shale cliffs near Lutengela, Van Jaarsveld, Xaba, Harrower & Zwide 58 (PRE! holotype)

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 diameter, leathery, dark green, subterete, slightly channelled on the adaxial side, finely striate with minute hairs. Inflorescence long racemose, the peduncle 25 ‒ 40 cm long, the raceme long and lax, up to 20 cm long, with 20 ‒ 50 nodding flowers, pedicels 14 ‒ 20 mm long; the peduncle and pedicels long persistent and photosynthetic after seeds dispersal lasting from flowering time in spring to autumn. Bracts lanceolate, acute, 3 ‒ 5 mm long, the lowermost with a long basal spur up to 8 ‒ 9 mm long; bracteoles absent. Flowers pentacyclic, trimerous, stellate, nodding, opening in the afternoon. Tepals 6, biseriate, free from the base, outer tepals lanceolate, 10 ‒ 11 × 2.5 ‒ 2.8 mm, inner tepals oblong-lanceolate, 9 ‒ 10 × 3 ‒ 3.5 mm; adaxial side of tepals white with a green macula at the base that connect to form a green basal perigone ring; abaxial side of tepals white with a narrow central and longitudinal green band, the perigone also showing a green basal ring. Stamens 6, filaments flattened and connate along most of their length to form a distinct erect tube of ca. 3.5 mm long around the gynoecium, ending in short triangular lobes of ca. 1 mm long that bear free sagittate anthers of ca. 3 mm long and 0.8 mm wide at the base, dehiscing by minute apical pores and connivent to the style. Ovary ovoid, trigonous, ca. 2.8 × 1.8 mm, green. Style narrow, erect, ca. 4.5 mm long, straight, mostly included in the filaments tube and the connivent anthers, elongating to overtop the anthers after dehiscence of the latter. Stigma small and indistinctly trigonous. Capsule triloculate, loculicide, 7 ‒ 10 × 5.4 ‒ 7.5 mm, valves splitting to the base. Seeds numerous, flattened, suboblong, L-H-W 5.3 ‒ 5.6 × 2.2 ‒ 2.5 × 1.2 ‒ 1.4 mm, black, with sinuous anticlinal testa cell walls ( Figs. 1 ‒ 2 ).

Etymology:— Aulostemon (Aulos, Greek name = tube, flute; - stemon, Greek = stamens). Named after its characteristic flowers, which show the filaments of stamens connate in a long tube.

Ecology and biogeography:—Rocky grasslands and crevices of vertical shale cliffs, usually south-facing, in thicket vegetation patches, associated with the Eastern Valley Bushveld and Bhisho Thornveld ( Mucina & Rutherford 2006), in subtropical region characterised by summer rainfall and few rains in winter (total yearly precipitation ca. 500 − 1000 mm), and infrequent occurrence of frost.

Distribution:—Eastern parts of the Eastern Cape Province of South Africa, only known from NW of Port St. Johns along the Mzimvubu (uMzimvubu) River gorge.

Taxonomic and phylogenetic notes:— Martínez-Azorín et al. (2013b) described Sagittanthera to include S. cyanelloides and S. mzimvubuensis based on the unique syndrome of morphological characters and the general appearance of their flowers, especially regarding the androecium morphology that is linked to buzz pollination, and similar biogeography.At the time of the description of Sagittanthera , these authors studied living material in cultivation of S. cyanelloides , from which the buzz pollination experiments were performed, but no living material was available of S. mzimvubuensis . We were recently able to study living plants from the type locality of this latter species in cultivation ( Fig. 1 ). This study evidences important morphological differences between the two species of Sagittanthera regarding characters that have been used in other subfamilies of Hyacinthaceae to segregate genera, such as connation of filaments and anthers, colour of tepals or presence of bracteoles ( Table 1). Sagittanthera was described as having connate anthers ( Martínez-Azorín et al. 2013b). However, the study of fresh material of S. mzimvubuensis revealed that the anthers in this latter species are free but connivent to the style ( Fig. 1D, G ), a character overlooked when studying photographs and herbarium material by Martínez-Azorín et al. (2013b). This renders the connation of the anthers along their distal half as a unique morphological character of S. cyanelloides in the whole family Hyacinthaceae , making recognition of Sagittanthera in a narrow sense very easy. Another interesting difference between the two Sagittanthera species is the presence of green basal maculae on the adaxial side of tepals in S. mzimvubuensis that form a green ring at the base of the perigone ( Fig. 1 ). This is also present on the abaxial side of perigone in a lower degree, whilst the adaxial side of tepals in S. cyanelloides is white (sometimes the darker longitudinal dorsal band of tepals is somewhat visible). The presence of green basal maculae of tepals has been used to recognize the recently described genus Mucinaea M.Pinter, Mart. -Azorín, U.Müll.-Doblies, D.Müll.-Doblies, Pfosser & Wetschnig in Pinter et al. (2013: 296), that is easily distinguishable by its purplish-pink tepals bearing a double-eyed green floral marking at their base, surrounded by a white margin, unique within Hyacinthaceae ( Pinter et al. 2013) . The presence of green maculae in S. mzimvubuensis also supports its independence from Sagittanthera in a narrow sense, being also unique within subfamily Urgineoideae , although the green markings in S. mzimvubuensis are different from those in Mucinaea . The presence of bracteoles has also been described as a general character of Sagittanthera ( Martínez-Azorín et al. 2013b) . However, S. mzimvubuensis lacks bracteoles, therefore differing from the type species in a character used for generic circumscription in Hyacinthaceae ( Speta 1998a, 1998b, 2001, Martínez-Azorín et al. 2011). Moreover, filaments of stamens in both species of Sagittanthera are very different. Whilst S. cyanelloides presents free filaments that are much shorter than the connate anthers, S. mzimvubuensis exhibits a long tube formed by the connation of the filaments that surrounds the gynoecium, supporting free but connivent anthers. Connation of filaments was the base to recognize genera in other subfamilies, such as Neopatersonia Schönland (1912: 251) ( Martínez-Azorín et al. 2011). It is therefore remarkable, that S. mzimvubuensis is unique within subfamily Urgineoideae in having connate filaments allowing easy identification and supporting the description of a new monotypic genus. Other differences in vegetative characters between the two species of Sagittanthera regard the formation of threads in the bulb scales of S. cyanelloides when broken (not produced in S. mzimvubuensis ), the broad, flattened and distinctly keeled leaves of S. cyanelloides (narrower and subterete in S. mzimvubuensis ), and the long persistent and photosynthetic stem and pedicels of the inflorescence after seeds release in S. mzimvubuensis (not soon withering after flowering in S. cyanelloides ). These character states also evidence the morphological differences between both species. Our phylogenetic studies based on three plastid regions (ycf, matK and trnL-trnF) and a nuclear one (Agt1) include more than 300 samples of Urgineoideae covering its whole distribution and most of the recognized species (M. Martínez-Azorín and collaborators, in preparation). Our results (not shown) recover S. cyanelloides and S. mzimvubuensis in isolated positions within the subfamily and placed far from each other (M. Martínez-Azorín and collaborators, in preparation). Whilst S. cyanelloides is located as sister to Thuranthos and Urginavia Speta (1998b: 86) , S. mzimvubuensis forms a different branch sister to Rhadamanthopsis ( Obermeyer 1980: 137) Speta (1998b: 74) . According to the data shown above, remarkable morphological and genetic differences existing between S. cyanelloides and S. mzimvubuensis support their segregation as two distinct genera, and therefore, the description of the new genus Aulostemon to accommodate the former S. mzimvubuensis . Inclusion of Sagittanthera cyanelloides in a single genus together with Thuranthos and Urginavia would be highly disruptive, as both latter genera show very different flower morphology and free anthers. On the other hand, although Aulostemon ( A. mzimvubuensis ) is sister to Rhadamanthopsis ( Obermeyer 1980: 137) Speta (1998b: 74) , the latter genus has campanulate nodding flowers with connate tepals, and free filaments (in part adnate to the perigone tube) and anthers, what does not allow inclusion of A. mzimvubuensis .

Figures

FIGURE 1. Aulostemon mzimvubuensis (Van Jaarsv.) Mart.-Azorín et al. in cultivation from the type locality, lower Mzimvubu River, near Lutengela, Eastern Cape Province of South Africa on 28 May 2014. A. Inflorescence; B. Young inflorescence showing bracts and long spurs; C. Flower, apical view; D. Flower with dissected androecium, lateral view; E. Flowers, adaxial (left) and abaxial (right) sides; F. Tepals, inners above and outers below, abaxial (left) and adaxial (right) sides; G. Androecium and gynoecium, dissected androecium on the right side, lateral views. Scale bars: 5 mm.

FIGURE 2. Seed of Aulostemon mzimvubuensis (Van Jaarsv.) Mart.-Azorín et al. in cultivation from the type locality, lower Mzimvubu River, near Lutengela, Eastern Cape Province of South Africa. Scale bar: 1 mm.