Solanum arundo Mattei, Boll. Reale Orto Bot. Palermo 7: 188. 1908.

Aubriot, Xavier & Knapp, Sandra, 2022, A revision of the " spiny solanums " of Tropical Asia (Solanum, the Leptostemonum Clade, Solanaceae), PhytoKeys 198, pp. 1-270 : 1

3. Solanum arundo Mattei, Boll. Reale Orto Bot. Palermo 7: 188. 1908.

Fig. 6

Solanum diplacanthum Dammer, Bot. Jahbr. Syst. 48: 245. 1912. Type. Tanzania. Sin. loc., Dr. Fischer s.n. (type: B?, destroyed, no duplicates found).

Solanum helleri Standl., Smithsonian Misc. Collect. 68, no. 5: 15. 1917. Type. Kenya. Rift Valley: Northern Frontier: Ewaso Ngiro River, Neumann’s Camp, 26 Sep 1911, E. Heller s.n. (holotype: US [00027596, acc. # 634351]).

Type.

Somalia. Banaadir: Mogadischo , 30 May 1913, G. Paoli 137 (neotype, designated by Vorontsova and Knapp 2016, pg. 74: FT [ FT003945 ]; isoneotype: FT [ FT003946 ]) .

Description.

Erect shrub to small tree, 2-6 m, densely prickly. Young stems erect, robust, densely stellate-pubescent and densely prickly, with porrect to multangulate, variously stalked trichomes, the stalks to 0.15 mm long, the rays 7-8(-15), 0.05-0.2 mm long, the midpoints reduced or absent, the prickles 5-10 mm long, 2.5-8 mm wide at the base, strongly curved, flattened, pale yellow to orange, densely stellate-pubescent in the lower 1/3; bark of older stems glabrescent to moderately stellate-pubescent, reddish brown. Sympodial units plurifoliate. Leaves simple, lobed, the blades 2-4(-7) cm long, 1.5-2.5(-3.5) cm wide, 1.5-2 times longer than wide, elliptic, concolorous, armed with 2-5 acicular, straight prickles to 12 mm long on both surfaces; adaxial surface glabrescent, with trichomes only at the base or along the midvein; abaxial surface glabrescent to sparsely stellate-pubescent with porrect, sessile or stalked trichomes, the stalks to 0.2 mm long, the rays 7-9, 0.1-0.2 mm long, the midpoints to 0.3 mm long; principal veins 3-5 pairs, further venation not visible or faint; base cuneate to rounded; margins lobed, the lobes 2-4 on each side, 0.2-0.7(-1.5) cm long, deltate to ovate, sometimes with secondary lobing, apically rounded, sometimes obtuse, the sinuses extending 1/4-2/3 of the distance to the midvein; apex broadly acute to rounded; petiole 0.05-0.5 cm long, less than 1/5 of the leaf blade length, densely stellate-pubescent, unarmed or with a few prickles. Inflorescences apparently lateral, 2-3(-4) cm long, unbranched or forked, with 2-8 flowers; 1-3 flowers open at any one time, densely stellate-pubescent, with 0-2 prickles; peduncle 0-4 mm long; pedicels 0.45-1 cm long, erect, articulated at the base, densely stellate-pubescent, unarmed; pedicel scars spaced 1-4 mm apart. Flowers 5-merous, heterostylous and the plants andromonoecious, with the lowermost 1-2 flowers long-styled and hermaphrodite, the distal flowers short-styled and staminate. Calyx 5.5-9 mm long, the lobes 3-4 mm long, deltate, apically acute to acuminate, sparsely stellate-pubescent, unarmed or with a few prickles. Corolla 2-3.2 cm in diameter, mauve to purple, stellate, lobed for ca. 4/5 of its length, the lobes 7-14 mm long, 3.5-4.5 mm wide, narrowly deltate, spreading, densely stellate-pubescent abaxially, the trichomes porrect, sessile or stalked, the stalks to 0.2 mm, the rays 6-9, 0.2-0.3 mm long, the midpoints reduced or to 0.5 mm long. Stamens equal; filament tube ca. 1.5 mm long; free portion of the filaments 0.5-1.5 mm long; anthers ca. 5.5 mm long, yellow, connivent, tapering, poricidal at the tips, the pores not lengthening to slits with age. Ovary densely stellate-pubescent in the upper 1/3; style 13-17 mm long in long-styled flowers, stout, curved, weakly stellate-pubescent in the lower 1/3, ca. 2 mm long in short-styled flowers; stigma clavate, minutely papillate. Fruit a globose berry, 1-2 per infructescence, 1.8-3 cm in diameter, the pericarp smooth, dark green with pale green and cream markings when young, yellow at maturity; fruiting pedicels 0.8-1.5 cm long, 1.5-2 mm in diameter at the base, woody, pendulous, usually unarmed but occasionally with a few prickles; fruiting calyx not markedly accrescent, but elongating to 7-12 mm long, somewhat fleshy and covering ca. 1/4 of the mature fruit (reflexed in herbarium sheets and on old fruits), unarmed or with up to 10 prickles. Seeds ca. 20-40 per berry, 2.2-3.2 mm long, 1.8-2.2 mm wide, flattened-reniform, dull yellow to orangish brown, the surfaces minutely pitted, the testal cells sinuate in outline. Chromosome number: not known.

Distribution

(Fig. 7 ). Solanum arundo is an African species, found primarily in eastern Africa from Somalia to Tanzania, in tropical Asia it occurs only in far western India on the Kathiawar peninsula in the state of Gujarat.

Ecology and habitat.

Solanum arundo is a plant of grasslands and savannahs in Africa ( Vorontsova and Knapp 2016); in India it is found in seaside vegetation ( Sen Gupta 1963).

Common names and uses.

There have been no common names or uses recorded for S. arundo , but in Africa it is often used as a hedge plant, due to its ability to form thick impenetrable thickets ( Vorontsova and Knapp 2016).

Preliminary conservation status

( IUCN 2019). Least Concern (LC); EOO (1,277,240 km2), AOO (216 km2). Solanum arundo has a broad distribution in Africa, and although it is relatively poorly represented in India, it is not of particular conservation concern based on its worldwide distribution. The distribution and occurrence of S. arundo on the Kathiawar peninsula need to be confirmed with modern collections.

Discussion.

Solanum arundo is a distinctive small extremely prickly tree, in Africa it is often associated with human habitation ( Vorontsova and Knapp 2016). It is easy to distinguish from other spiny solanums in western India by the combination of thick, curved, and flattened prickles on the densely stellate- or multangulate-pubescent stems, and long, straight prickles on the leaves. Solanum forskalii is sympatric with S. arundo and has similar white-pubescent stems, but it is a smaller, scandent plant, with truncate to cordate rather than cuneate leaf bases, smaller corollas (1.3-2.4 versus 2-3.2 cm in diameter) and much smaller fruits (0.6-0.9 versus 1.8-3 cm in diameter). In 2018, one of us (SK) erroneously identified the specimens of S. arundo in CAL as S. forskalii (Fig. 6 ).

Vorontsova et al. (2013) resolved S. arundo as sister to the more narrowly distributed African endemic S. dennekense Dammer, a similar treelet with curved stem spines, white stems, and large, leathery berries.

Sen Gupta (1963) suggested that S. arundo had arrived in India with Arab traders in the nineteenth century, as part of the extensive Gujarati trade routes established across the Arabian Sea. Its restricted distribution on the Kathiawar peninsula certainly supports this idea. Solanum arundo has not been collected, to our knowledge, since the 1960s, re-evaluation of its presence and distribution in western India is necessary.

Specimens examined.

See Suppl. materials 1-3.

Figures

Figure 6. Solanum arundo Mattei A herbarium specimen collected in India in 1963 (Safni CNH- 2488) B detail view of flower (Vorontsova et al. 80, Kenya) C detail view of fruit (Vorontsova et al. 80, Kenya). Photograph credits: A © The Director, Botanical Survey of India, Kolkata B, C M. S. Vorontsova.

Figure 7. Distribution of S. arundo.