Solanum nelsonii
Citation:
Prodr. [A.P. de Candolle] 13(1): 123. 1852.
Type:
United States of America: Hawai'i: "Hawaiian Islands", D. Nelson s.n. (holotype: BM [BM000846708]).
Written by:
Donald H.R. McClelland (2012)
Habit:
Unarmed prostrate shrub, the internodes to 5.8 mm long. Stems densely pubescent with yellow-ferruginous, short-stipitate porrect stellae, stipes of various lengths to ca. 0.2 mm, the stellae persistent, 0.7–0.8 mm broad, with 8–11 rays, the midpoint erect or flexed at the base ±90°, shorter than the rays; a transparent sloughing layer absent on young stems.
Sympodial structure:
Sympodial units trifoliate, though more often appearing tetrafoliate, not geminate.
Leaves:
Leaves simple, the blades 2.3–6.4 × 2.1–6.2 cm, ±as long as wide, ovate, orbicular, oval, to deltoid or cordate, chartaceous to sub-coriaceous, densely pubescent above with short-stipitate porrect stellae when young, densely pubescent when mature, the stellae 0.5–0.7 mm in diameter, with 7–9 rays, the stipes to 0.2 mm long, the midpoint of the stellae erect or curved, shorter than the rays, densely pubescent below with short-stipitate porrect stellae when young, densely pubescent when mature, the stellae 0.4–1.2 mm in diameter, with 7–9 rays, the stipes to 0.2 mm long, the midpoint of the stellae erect, shorter than the rays; blade with 4–6 veins on either side of the midvein, the midvein raised abaxially, distinct adaxially, the lateral veins weakly brochidodromous, raised abaxially, distinct adaxially; blade base cordate to rounded, aequilateral; margin entire or very occasionally lobed; apex obtuse; petiole 1.0–3.4 mm long, 1.1–1.8 mm in diameter, channeled above, densely pubescent all over.
Inflorescences:
Inflorescence to 7.6 cm long in flower, observed to 3.6 cm long in fruit but presumably at least equal to length in flower, appearing lateral, extra-axillary, emerging from the 1/3 of the internode, unbranched, with 7–17 flowers, all apparently fertile or potentially so, the axes densely pubescent, stipitate porrect stellae; peduncle in flower observed 10.3–14.5 mm long but presumably as short as in fruit, 0.9–1.0 mm in diameter, in fruit 8.0–33.1 mm long, 1.3–1.7 in diameter; pedicels 1.2–1.9 cm long, 0.6–0.9 mm in diameter at the base, 1.1–1.5 in diameter below the calyx, straight, bent to ±90° below the calyx, gradually increasing in diameter in the distal ca. 1/4, densely pubescent, the bases well spaced to 1.8 mm apart in flower, 1.9–2.6 cm long, 0.8–1.1 mm in diameter at the base, 1.9–2.7 mm in diameter below the calyx, straight or arching, not bent below the calyx, gradually increasing in diameter in the distal 1/4–1/3, with a distinct bulge directly below the calyx, densely pubescent, the bases well spaced to 1.8 cm apart in fruit, rigid, in two rows, articulate at the base. Buds globose, the calyx densely stellate-pubescent, the corolla densely stellate-pubescent, the surface of the corolla of the mature bud ridged.
Flowers:
Flowers heterostylous, 5-merous. Calyx 2.8–4.2 mm long, with deltoid lobe tips, the tube 1.7–2.8 mm long, the lobe tips 0.9–1.5 × 1.2–1.4 mm, the intersepalar tissue opaque when dry; splitting in the sinuses during fruit development and then the lobes dentate, at anthesis densely pubescent abaxially, densely pubescent at the apex, glabrous towards the base adaxially, the calyx lobes in fruit 4.3–6.2 × 3.2–3.5 mm, densely pubescent, appressed. Corolla 1.3–1.7 cm in diameter, stellate with well-developed, glabrous interpetalar tissue, purple or the interpetalar and petalar tissue white with purple veins, the lobes 4.1–6.3 × 4.3–4.8 mm, deltoid, the midrib 5.7–7.8 × 3.1–3.8 mm, lanceolate, densely pubescent abaxially, glabrous adaxially, spread wide at anthesis. Stamens adnate to the corolla, the free portion of the filament ca. 1.2 mm long; anthers 2.8–2.9 × 0.9–1.2 mm, acuminate, arcuate, markedly attenuate, yellow to dark purple appearing nearly black, spreading, with minute apical pores, the pores directed distally, extending around the edge of the apex, the lateral sutures entire or perforated, remaining intact with age. Ovary 0.7–1.3 mm, globose, white to cream, densely pubescent at the apex, glabrous towards the base; short styles ca. 1.5 mm long, ca. 0.2 mm in diameter, cylindrical, shorter than the stamens, long styles 3.5–4.8 mm, ca. 0.2 mm in diameter, filiform, longer than the stamens, emerging between the anther apices, straight, the basal ¼ moderately pubescent; stigma ca. 0.3 mm in diameter, capitate, green.
Fruits:
Fruit a berry, 0.8–1.3 cm in diameter, globose, the immature fruits evenly green, black when mature, glabrous; exocarp thin, glossy; endocarp juicy.
Seeds:
Seeds many per fruit, 2.2–2.9 × 2.3–3.3 mm, flattened-orbicular and notched at the point of attachment to flattened-reniform, red-brown to yellow-brown when dry, the surface evenly reticulate all over.
Chromosome number:
Not known
Distribution:
Solanum nelsonii used to occur on several of the main islands of Hawaii in addition to the leeward islands. Now it is restricted to Moomomi Dunes on Molokai where it grows in shifting and fixed sand dunes and in central areas of some of the leeward islands from 2–10 m elevation. The sea side is not a typical location for Solanums; S. nelsonii is the only Solanum known to live in shifting dunes.
Phenology:
Known to flower January–June, August–October, and December and fruit January–June and August–September, but likely flowering and fruiting year round.
Phylogeny:
Solanum nelsonii is a member of subgenus Leptostemonum ( the spiny solanums) and within that clade is a member of section Irenosolanum.
References:
Wagner, W.L., D.R. Herbst & S.H. Sohmer. 1999. Solanaceae. Manual of the Flowering Plants of Hawaii. University of Hawaii Press, Honolulu, Hawai'i.
Conservation status:
Vulnerable (Wagner et al. 1999)
The most striking characteristic of S. nelsonii besides its unusual habitat preference is its habit—a mat forming prostrate shrub, unique within section Irenosolanum. Solanum nelsonii is most similar to S. caumii but differs in habit, leaf length to width ratio, sometimes in fruit color, and habitat preference. Wagner et al. (1999) listed S. nelsonii (including S. caumii) as vulnerable. Following the segregation of S. caumii herein, the conservation status of S. nelsonii may need to be reassessed as recognizing S. caumii effectively reduces the population size of S. nelsonii.
This species is named in honor of the botanist David Nelson, who in addition to another fateful voyage, participated in Captain Cook’s third and final voyage to the Pacific. The type of this species was collected by David Nelson on that voyage.