Solanum retrorsum Elmer, Leaflets Philipp. Bot. 1: 342. 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

37. Solanum retrorsum Elmer, Leaflets Philipp. Bot. 1: 342. 1908.

Fig. 63

Solanum luzoniense Merr., Philipp. J. Sci. Bot. 13: 58. 1918. Type. Philippines. Ilocos: Luzon, Central Luzon, Pangasinan Province, Mount Umingan, Aug 1910, M. Ramos & G.E. Edaño [Bur. Sci.] 26487 (lectotype, designated here: K [K000195878]; isolectotype: US [acc # 1376054, US00027662]).

Solanum luzoniense Merr. var. glabrum Merr., Philipp. J. Sci. Bot. 13: 59. 1918. Type. Philippines. Ilocos: Luzon, Central Luzon, Pampanga Province, Calumpit, Sep 1905, E.D. Merrill 4237 (lectotype, designated here: K [K000195959]; isolectotype: US [acc # 710167, US00027663]).

Type.

Philippines. CAR: Luzon , Benguet Province, Baguio, Mar 1907, A.D.E. Elmer 8719 (lectotype, designated here: K [K000195910]; isolectotypes: A [0077850], E [E00243613]) .

Description.

Shrubs or scrambling shrubs to 1.5 m, armed or unarmed. Stems erect, terete, prickly or unarmed, moderately stellate-pubescent; prickles if present 3-5 mm long, straight (occasionally somewhat slightly curved) and downwardly pointing (retrorse), yellowish tan; pubescence of mixed sessile and short-stalked porrect-stellate trichomes, the stalks to 0.2 mm, the rays 6-8, ca. 0.5 mm long, the midpoints equal to the rays, the trichomes persistent or deciduous and the stems glabrate; new growth moderately to densely stellate-pubescent, the trichomes whitish cream, mixed sessile and short-stalked porrect-stellate like those of the stems; bark of older stems whitish grey. Sympodial units plurifoliate, the leaves not geminate. Leaves simple, not lobed or occasionally very shallowly lobed, the blades 3-15 cm long, 1-6 cm wide, 2-3 times longer than wide, narrowly elliptic to lanceolate, widest at the middle, chartaceous, somewhat discolorous, usually unarmed; adaxial surface glabrous to moderately and evenly stellate-pubescent with mixed sessile and short-stalked porrect-stellate trichomes, the stalks to 0.2 mm, the rays 6-8, ca. 0.5 mm long, the midpoints equal to the rays; abaxial surface similarly but more densely pubescent with porrect-stellate trichomes, the lamina still visible; major veins 5-7 pairs, barely visible above, stellate pubescent especially abaxially; base attenuate, usually somewhat oblique; margins entire or rarely very shallowly lobed, the lobes 1-2 on each side, ca. 0.5 cm long, broadly deltate with rounded or acute tips, the sinuses reaching less than 1/8 of the distance to the midrib; apex acute to acuminate; petioles 0.6-2.5 cm long, ca. 1/4 as long as the leaf blades or less, unarmed and densely stellate-pubescent with mixed sessile and short-stalked porrect-stellate trichomes like those of the stems, pubescence denser than that of stems. Inflorescences 1.5-4.5 cm long, internodal and lateral, unbranched or very occasionally forked, with 10-30 flowers, only a few flowers open at any one time, sparsely to densely pubescent with porrect-stellate trichomes like those of the stems; peduncle 0.3-0.8 cm long, to 1.5 cm long on each of the inflorescence branches; pedicels 0.6-0.75 cm long, ca. 0.5 mm in diameter at the base, ca. 0.5 mm in diameter at the apex, spreading and perhaps slightly nodding at anthesis, stellate-pubescent with porrect-stellate trichomes like the inflorescence, articulated at the base; pedicel scars irregularly spaced 2-4 mm apart. Buds elongate and tapering, approximately halfway exserted from the calyx before anthesis. Flowers 5-merous, apparently all perfect. Calyx with the tube 1.5-2 mm long, conical, the lobes 2-2.5 mm long, ca. 2 mm wide, deltate to narrowly deltate, densely stellate-pubescent like the pedicels. Corolla 1-1.4 cm in diameter, white, stellate, lobed nearly to the base, the lobes 4-7 mm long, 3-4 mm wide, narrowly triangular, spreading at anthesis (perhaps slightly reflexed?), glabrous adaxially, moderately stellate-pubescent abaxially where exposed in bud. Stamens equal; filament tube minute, glabrous; free portion of the filaments ca. 0.5 mm long, glabrous; anthers 3-4.5 mm long, 1-1.2 mm wide, strongly tapering, yellow, poricidal at the tips, the pores directed distally, not elongating to slits with drying. Ovary conical, glabrous; style 6-8 mm long, glabrous or with a few stalked stellate trichomes near the base; stigma capitate, the surfaces minutely papillose. Fruit a globose berry, 0.6-0.8 cm in diameter, bright red when ripe, the pericarp thin and shiny, glabrous; fruiting pedicels 0.8-1.8 cm long, 0.7-1.1 mm in diameter at the base, 1.5-2 mm in diameter at the apex, somewhat woody, erect or somewhat spreading; fruiting calyx not accrescent, the lobes often breaking off. Seeds 6-10 per berry, 3.5-5 mm long, 1.5-3.5 mm wide, flattened reniform with incrassate margins, yellowish tan, the surfaces minutely pitted, the testal cells with sinuate margins. Chromosome number: not known.

Distribution

(Fig. 64 ). Solanum retrorsum occurs from the very northern part of Sulawesi (a single collection) in Indonesia to the Philippines, where it is much more common. The single collection from Lanyu (Orchid) Island off the southeastern edge of Taiwan is a very poor specimen and is included here with some hesitation.

Ecology and habitat.

Solanum retrorsum grows in thickets, forests and forest edges in broadleaf evergreen and semideciduous woodlands; few of the collections we have seen have specific habitat information; elevations from 500 to1,600 m elevation.

Common names and uses.

Taiwan. lü song qie ( Zhang et al. 1994, as S. luzoniense , but this identification is tentative).

Preliminary conservation status

( IUCN 2019). Near Threatened (LC). EOO (115,321 km2, LC); AOO (48 km2, EN). Solanum retrorsum is found throughout the Philippines, with populations in a variety of habitats. The range extends to Sulawesi, making it widely distributed. The status of populations outside the main range in the Philippines, however, needs further investigation and the few recent collections suggest that the species merits some conservation concern.

Discussion.

Solanum retrorsum is polymorphic for prickliness; some plants are densely prickly with the downward point prickles that give the species its name, while others lack prickles entirely. These unarmed plants have been called S. luzoniense. Despite this polymorphism S. retrorsum is distinctive, with its narrowly elliptic leaves and very small ripe berries, and not easily confused with any other species in the region.

The polymorphism in prickliness seen in S. retrorsum is also found in S. ratale D.McClelland of Fiji (see McClelland et al. 2020). That species also has unarmed and densely prickly individuals with strongly retrorse prickles mainly on the stems; the plurifoliate sympodial units, trichomes with midpoints equal to the rays and bright red berries (versus difoliate sympodia, small trichomes with elongate midpoints and black to deep purple berries in S. ratale ), as well as their distinct distributions, clearly distinguish the two species.

The description of S. luzoniense in Zhang et al. (1994) was taken from a mixture of material from Taiwan and the Philippines. Material from Taiwan was a mixture of S. miyakojimense (Yang 8701) and a very scrappy specimen from Lanyu Island (Leu et al. 2118) that we here tentatively assign to S. retrorsum , but with considerable hesitation. The occurrence of S. retrorsum in Taiwan remains to be confirmed.

Merrill (1918b) did not specifically designate a type for his S. luzoniense . He cited "Bur. Sci. 24687 Ramos & Edaño”, "Bur. Sci. 17710 Otanes" and "Merrill s.n., July 1903"; we have selected the Kew duplicate of Ramos & Edaño [Bur. Sci.] 26487 (K000196878) as the lectotype because it is well preserved and has both flower and fruit. For var. Solanum luzoniense glabrum , he clearly stated that his own collection (Merrill 4237) was the type but did not specify the herbarium. We have selected the Kew duplicate of this collection (K000195959) as the lectotype of the varietal name because it is the best-preserved specimen of all the duplicates we have seen.

Specimens examined.

See Suppl. materials 1-3.

Figures

Figure 63. Solanum retrorsum Elmer - Herbarium specimen collected in the Philippines in 1914 (Merrill 9665, K 000195908) Photograph credit: © copyright of the Board of Trustees of the Royal Botanic Gardens, Kew.

Figure 64. Distribution of S. retrorsum.