Overview

Distribution

Solanum acanthodapis is endemic to the extreme north-east of New South Wales, around Lismore. It grows in canopy-gaps in notophyll rainforest, usually on basaltic clay-loams, but also on meta-sediments. It is endemic to the area formerly covered by the Tweed Shield Volcano, centered on the plutonic complex of Mount Warning.

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Physical Description

Diagnostic Description

Formal Description

Habit

Prostrate, stoloniferous perennial shrub up to 0.3 m tall. Juvenile stage absent. Stems terete or ridged, brown, sparsely to densely stellate-pubescent, the stellae 0.2-0.35 mm in diameter, sessile, the lateral rays 7-8, porrect, the midpoints 0.5-1.5 times as long as lateral rays, eglandular; finger hairs absent; very short, gland-tipped hairs hairs absent; prickles straight, acicular, 3-7 mm long, 9-20 times longer than wide, 25-65 per dm.

Sympodial Structure

Sympodial units probably difoliate, the leaves geminate or not.

Leaves

Leaves simple, the blades 5.5-9.5 x 2.8-4.5 cm, 1.6-2.3 times as long as wide, elliptical or ovate, chartaceous, green and glabrous to sparsely stellate-pubescent adaxially, the stellate hairs confined to midrib; finger hairs absent; very short, gland-tipped hairs absent; prickles present on midvein and lateral veins, 20-60, straight, acicular, 2-8 mm long; green to white or yellowish and sparsely to very densely stellate-pubescent abaxially, the hairs spaced 0.05-0.25 mm apart, 0.25-0.35 mm in diameter, sessile, the lateral rays 7-8, porrect, the midpoints 0.2-0.8 times as long as lateral rays, eglandular; finger hairs absent; very short, gland-tipped hairs absent; prickles present on midvein and lateral veins, 10-30, straight, acicular; base cuneate or obtuse, the oblique part 0-5 mm long; margin entire or shallowly lobed throughout, the lobes 2-4 on each side, acute, lobing index 1-1.4; apex acute; petioles 1-1.7 cm long, 14-29% length of lamina, sparsely to densely stellate-pubescent, prickles present.

Inflorescences

Inflorescence up to 1 cm long, extra-axillary, unbranched, pseudo-umbellate or pseudo-racemose, with 2-8 flowers, the plants strongly or weakly andromonoecious, the axes sparsely to densely stellate-pubescent, armed or unarmed; peduncle 0-0.7 cm; rachis 0.2-0.3 cm; pedicels 6-20 mm long in flower, 0.25-0.4 mm thick throughout, 21-30 mm long in fruit, ca. 0.8 mm thick, spaced 1-2 mm apart, articulated at the base.

Flowers

Flowers heterostylous, 5-merous. Calyx 5-6 mm long, the tube 2-3 mm long, the lobes 1.5-3.5 mm long, attenuate, moderately stellate-pubescent, the hairs transparent or purple, 0.2-0.3 mm across, sessile, the lateral rays 7-8, the midpoints 0.5-1 times as long as laterals, eglandular; finger hairs absent; very short, gland-tipped hairs absent; prickles present or absent, 0-5 per flower, 0.5-2 mm long; fruiting calyx with lobes less than half length of mature fruit, armed or unarmed. Corolla 1.5-2.5 cm in diameter, 8-12 mm long, shallowly lobed, with sparse interpetalar tissue, chartaceous, pinkish or purple, the tube 3-5 mm, the lobes 9-10 x 4-6 mm, narrowly triangular, moderately stellate-pubescent abaxially on center of lobes, glabrous adaxially and on interpetalar tissue. Stamens with filaments 0.5-1.5 mm; anthers 4-5 x 1-1.5 mm at base, narrowly ovate, slightly tapered, not or loosely connivent, yellow, the pores minute and directed distally. Ovary with very short, gland-tipped hairs on distal half; functional style 6-7.5 x 0.5-1 mm, cylindrical, glabrous or with very short, gland-tipped hairs at base; stigma capitate.

Fruits

Fruits 1 per inflorescence, 1.5-1.8 cm in diameter, 1-locular (septum absent or incomplete), globose, yellowish-green, glabrous, the exocarp ca. 0.8 mm thick, the mesocarp moist but not juicy, the placenta in cross-section sessile, elliptical.

Seeds

Seeds 3.5-4 x 3-3.5 mm, whitish or pale yellow, flattened, the surface finely reticulate.

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Life History and Behavior

Cyclicity

Phenology

Flowers recorded between August and February; fruits in March and April.

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Evolution and Systematics

Systematics or Phylogenetics

Phylogeny

Solanum acanthodapis is a typical member of Solanum subgenus Leptostemonum. It is placed into the S. macoorai group (Group 27B) by Bean (2004) on morphological grounds; its phylogenetic position has not been investigated using molecular data. Bean (2002) postulates that it is most closely related to S. serpens.

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References and More Information

Commentary

Solanum acanthodapis is one of three Australian species that exhibit a unique prostrate and stoloniferous habit, with long runners rooting at the nodes and sporadic erect shoots. Well-developed plants of this species form a dense prickly carpet no more than 20 centimetres high. The fruits are borne virtually at ground level and hidden from view by the foliage. Bean (2004) did not observe any clues that would indicate the method of seed dispersal.

Solanum acanthodapis differs from S. serpens by: stellate hairs (on all parts) with short central rays (vs. very long central ray for S. serpens); upper leaf surface (excluding veins) glabrous even on developing leaves; lateral veins somewhat raised on upper leaf surface; ovary glabrous or with stipitate glandular hairs only (vs. stipitate glandular hairs and stellate hairs for S. serpens).

A collection from the property of Mr. B. Walker, southern outskirts of Nimbin (Bean 16948, BRI, MEL, NSW) is morphologically intermediate between S. serpens and S. acanthodapis.

Etymology: From the Greek acanthos (prickly) and dapis (a carpet or rug), alluding to the habit of the plant. Well-developed plants resemble a prickly green carpet.

Conservation status: Solanum acanthodapis is known from only four locations, with a total population certainly less than 10,000 individuals (and probably less than 1000 individuals). Applying the IUCN guidelines (IUCN, 2001), a category of “Vulnerable” is recommended (VU C2a(i)). It is threatened by weeds, clearing of its habitat, and destruction by humans.

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