Solanum medicagineum A.R.Bean, 2012

Bean, A. R., 2012, A taxonomic revision of the Solanum echinatum group (Solanaceae), Phytotaxa 57 (1), pp. 33-50 : 43-45

Solanum medicagineum A.R.Bean , sp. nov. ( Fig. 3 )

S. rhaphiotes affinis sed foliis minoribus latioribus, pilis stellatis minoribus calycis, pedunculo communi 3–9 mm longo, antheribus filamentisque brevioribus et aculeis paucioribus in calycibus fructiferis differens.

Type: — AUSTRALIA. Northern Territory: Fisher Creek, Kakadu National Park , 19 April 1990, G.J. Leach 2779 & I.D. Cowie (holotype BRI!; isotype DNA! ).

Prostrate shrub 0.1–0.3 m high. Juvenile branchlets with ca. 32 prickles per decimetre, 1.5–5 mm long; juvenile leaves broadly ovate, entire, 4.8–6 cm long, 3.7–4.9 cm wide. Adult branchlets grey, brown or purplish; prickles 25–120 per decimetre, straight, acicular, 1–6 mm long, 7–11 times longer than wide, with dense stellate hairs near base; stellate hairs very dense, 0.4–0.5 mm in diameter, the stalks 0–0.4 mm long, the central ray 0.8–1.2 times as long as laterals. Adult leaves simple, the blades broadly ovate, 2.1–3.8 cm long, 1.3–2.2 cm wide, 1.5–1.8 times longer than broad. Upper surface green or grey-green, prickles absent; stellate hairs dense to very dense, spaced 0.05–0.1 mm apart, 0.3–0.5 mm across, the stalks 0–0.25 mm long, the central ray 0.8–1.2 times as long as laterals. Lower surface white or grey, prickles absent; stellate hairs very dense, spaced ca. 0.05 mm apart, 0.4–0.6 mm diameter, the stalks 0–0.3 mm long, the central ray 0.8–1.3 times as long as laterals; entire, the base cuneate, obtuse or auriculate, the oblique part 0–3.5 mm long, obliqueness index 0–10 percent, the apex acute; petioles 0.9–2.2 cm long, 32–63% length of lamina, prickles present or absent. Inflorescence 1–2(–3)-flowered, with common peduncle 3–9 mm long, rachis prickles present; pedicels at anthesis 4–8 mm long, prickles present; calyx tube 2.5–3 mm long, the lobes deltate or attenuate, ca. 1 mm long; calyx prickles present at anthesis, ca. 20 per flower, 0.5–1 mm long; calyx stellae very dense, yellow or white, 0.25–0.35 mm across, the stalks 0–0.1 mm long, the central ray 0.8–1.2 times as long as laterals. Corolla purple, 7–9 mm long, the inner surface glabrous; anthers 2.7–3.1 mm long; free part of the filaments 0.6–0.8 mm long; style ca. 7 mm long, erect, protruding between anthers, glabrous. Fruiting calyx not completely surrounding fruit; stellate hairs all about the same size, stalks 0–0.3 mm long, protoprickles absent; prickles 40–70, 2– 6 mm long, often curved, with stellae extending to distal half of prickle; pedicels 8–14 mm long. Mature fruits solitary, oblate, 13–15 mm diameter. Seeds 1.8–2.0 mm long.

Distribution and habitat: — Solanum medicagineum is confined to the Northern Territory, where it occurs in Kakadu National Park, and around Mt Borradaile in Arnhem Land ( Map 1 ). It inhabits the gullies or upper slopes of sandstone bluffs, escarpment tops and plateaux. The soil is shallow and sandy.

Phenology: —Flowers and fruits have been recorded from January to June.

Etymology: —Derived from the genus name Medicago . There is a resemblance between the fruiting calyces of this species and the fruits of some species of Medicago .

Additional specimens examined (paratypes): — AUSTRALIA. Northern Territory: near UDP Falls, South Alligator, 20 February 1969, N. Byrnes NB1381 (DNA); ESE of Mudginberry, 19 February 1973, C.R. Dunlop 3300 (DNA); Mt Brockman , Kakadu National Park , 29 March 1995, J. Egan 4577 (DNA); UDP Falls, 7 miles [11 km] NW of El Sharana, 24 January 1973, R. Schodde AE544 ( CANB, DNA); 4.5 km SE of Mt Borradaile, 27 June 1992, S. Taylor 88 (DNA); Radon Creek , Mt Brockman , west Arnhem Land escarpment, May 1978, L. Webb & G. Tracey 13477 ( BRI).

Notes: —This species has a number of distinctive characteristics and its closest relative is unclear. For example, its fruiting calyces have relatively few and often curved prickles, and those prickles are largely clothed in stellate hairs; the adult leaves are unusually small (usually less than 3 cm long) and broadly-ovate; the inflorescences often comprise a single flower, although 2-flowered cymes (and rarely 3-flowered) are also found.

It differs from S. rhaphiotes by the smaller and broader leaves, the shorter anthers and filaments, the smaller stellate hairs of the calyx, the shorter rachis and peduncle, and the fewer prickles on the fruiting calyx. It differs from the partly sympatric S. lapidosum by the more prickly branchlets, the shorter leaves, the longer central ray on the stellate hairs on all plant parts, the shorter anthers and filaments, the erect style, and the fewer prickles on the fruiting calyx.

Figures

MAP 1. Distribution of Solanum echinatum (circles); Solanum wilkinsii (triangles); Solanum medicagineum (stars).

FIGURE 3. Solanum medicagineum. A. branchlet and leaves; B. corolla and stamens; C. calyx and pedicel at anthesis; D. ovary and style; E. a stellate hair from the branchlet; F. fruiting calyx surrounding dried fruit; G. a section of the fruiting calyx showing prickles and hairs. A–E from Dunlop 3300; F–G from Leach 2779 & Cowie. Scale bar: A = 12 mm, B = 3 mm, C = 1.5 mm, D = 1.5 mm, E = 0.25 mm, F = 6 mm, G = 1 mm.