Solanum caumii (F.Br.) D.McClelland, comb. et, 2020

McClelland, Donald H. R., Nee, Michael & Knapp, Sandra, 2020, New names and status for Pacific spiny species of Solanum (Solanaceae, subgenus Leptostemonum Bitter; the Leptostemonum Clade), PhytoKeys 145, pp. 1-36 : 1

Solanum caumii (F.Br.) D.McClelland, comb. et stat. nov. Figure 4

Solanum nelsonii Dunal var. caumii F.Br., Bull. Bish. Mus. 81: 36, pl. 15B. 1931. Type. United States of America. Hawaii: Leeward Islands, Nihoa, 75 m, 19 Jun 1923 (fl, fr), E. Caum 84 (holotype: BISH [acc. # 581193, barcode BISH1014622]; isotypes: BISH [acc. # 581194, barcode BISH1014623], K [K000922665], NY [00172288], UC [acc. #505079]).

Solanum nelsonii Dunal var. acuminatum F.Br., Bull. Bish. Mus. 81: 36, pl. 16A. 1931. Type. United States of America. Hawaii: Leeward Islands, Nihoa, 75 m, 19 Jun 1923 (fl, fr), E. Caum 68 (holotype: BISH [acc. # 581186, barcode BISH1014620]; isotypes: BISH [acc. # 581185, barcode BISH1014621], K [K000922664], NY [00172287]).

Type.

Based on Solanum nelsonii Dunal var. caumii F.Br.

Description.

Erect to sprawling shrub to ca. 1.5 m, the internodes to 6.6 cm long, unarmed. Stems densely pubescent with yellow-ferruginous, short-stalked porrect-stellate trichomes, the stalks of various lengths to ca. 0.1 mm, the rays 6-10, 0.15-0.2 mm long, the midpoint shorter than the rays; new growth densely stellate-pubescent; bark of older stems reddish brown. Sympodial units difoliate, the leaves geminate or not, if geminate the leaves of a pair similar in size and shape. Leaves simple or shallowly lobed; blades 3.5-8.0 cm long, 2.2-6.4 cm wide, 1.3-1.6 times as long as wide, deltate to ovate, chartaceous, concolorous, unarmed; adaxial surfaces densely pubescent with short-stalked porrect-stellate trichomes, the stalks to ca. 0.1 mm long, the rays 6-9, 0.1-0.2 mm long, the midpoint much shorter than the rays; abaxial surfaces densely pubescent with short-stalked porrect-stellate trichomes, the stalks to ca. 0.1 mm long, the rays 7-9, 0.2-0.25 mm long, the midpoint of the stellate trichomes much shorter than the rays; principal veins 4-6 pairs, the midrib raised abaxially, distinct adaxially, the lateral veins weakly brochidodromous or semicraspedodromous, raised abaxially, distinct adaxially; base cordate, truncate, or rounded; margins entire or shallowly lobed, the sinuses less than 1/4 of the way to the midrib; apex acute to acuminate; petiole 0.8-3.3 cm long, 1.0-1.4 mm in diameter, channeled adaxially, densely pubescent with stalked porrect-stellate trichomes like the stems and leaves. Inflorescence to 8.1 cm long in flower, appearing lateral, extra-axillary, emerging from the distal 1/3 of the internode, typically unbranched but occasionally forked, with 10-16 flowers, densely pubescent with short-stalked porrect-stellate trichomes like the stems and leaves; peduncle 0.5-1.7 cm long; pedicels 0.9-1.2 cm long, 0.3-0.6 mm in diameter at the base, 0.5-0.9 mm in diameter below the calyx, straight, densely pubescent with porrect-stellate trichomes like those of the inflorescence axes, articulated at the base; pedicel scars evenly spaced to 8.8 mm apart, in two rows. Buds globose, the calyx densely stellate-pubescent, the corolla densely stellate-pubescent abaxially where exposed, strongly exerted from the calyx before anthesis. Flowers 4-5-merous, heterostylous, with short-styled flowers borne distally, the plants weakly andromonoecious. Calyx 3.1-4.9 mm long, the tube 1.7-1.8 mm long, the lobes 1.1-3.5 mm long, 1.2-2.1 mm wide, deltate, splitting in the sinuses during fruit development and then the lobes long-triangular, densely pubescent abaxially and adaxially. Corolla 1.3-2.0 cm in diameter, stellate, white, the interpetalar tissue well-developed, glabrous, the petal midveins purple, the lobes 5.1-5.7 mm long, 7.2-7.4 mm wide, deltate, spreading at anthesis, moderately pubescent abaxially, more or less glabrous adaxially. Stamens equal; filament tube minute; free portion of the filaments ca. 1.5 mm long, glabrous; anthers 2.9-3.2 mm long, 0.8-0.9 mm wide, tapering, strongly arcuate and spreading, purple sometimes appearing almost black, poricidal at the tips, the pores directed distally, not splitting with age. Ovary ca. 0.8 mm in diameter, ovate, white or cream in live plants, densely pubescent with porrect-stellate trichomes; styles of long-styled flowers ca. 3.8 mm long, ca. 0.4 mm in diameter, exserted from the anther cone, filiform, straight, densely stellate pubescent in the basal 2/3, in short-styled flowers 2.1-2.5 mm long, 0.1-0.2 mm in diameter, included in the anther cone; stigma ca. 0.3 mm in diameter, capitate, white or cream (live plants). Fruit a globose berry, 1.0-1.5 cm in diameter, green when immature, red or black when mature, juicy, glabrous, the pericarp thin, matte to slightly glossy, opaque; fruiting pedicels 1.1-1.9 cm long, 0.9-1.1 mm in diameter at the base, 2.1-2.3 mm in diameter below the calyx, straight and spreading; fruiting calyx lobes 3.4-6.3 mm long, 1.8-2.5 mm wide, moderately to densely pubescent, appressed to the berry surface. Seeds 20-30 per fruit, 2.8-3.5 mm long, 3.5-4.1 mm wide, flattened-reniform, red-brown when dry, the surface minutely pitted and evenly reticulate, the testal cells straight-sided. Chromosome number not known.

Distribution and ecology

(Figure 5 ). Solanum caumii is restricted to the state of Hawaii (United States of America) on the tiny island of Nihoa in shallow rocky soil from 10 to 270 m elevation. Plants have been collected from both coastal and higher elevation areas on the island.

Phenology.

Known to flower March-April and June-September and fruit March and June-July.

Common names and uses.

United States of America. Hawaii (Nihoa): Akia (St. John 22731).

Etymology.

The epithet honors Edward Leonard Caum (1893-1952), the American botanist who collected the type.

Preliminary conservation assessment

( IUCN 2019). EOO = 0.25 km2 [CR - Critically Endangered]; AOO = 4 km2 [CR - Critically Endangered]. We assess Solanum caumii as CR (Critically Endangered) using IUCN Criteria of B1,2a,b; populations may be secure on the isolated island of Nihoa that is largely protected, but no recent studies on population stability have been undertaken. Recognition of S. caumii at the species level has conservation consequences. Symon (1999) included S. caumii within S. nelsonii . At that time S. nelsonii was listed as vulnerable; segregation of S. caumii the species may change the status of S. nelsonii . Threats to S. caumii include habitat destruction from natural causes and herbivory by an introduced grasshopper ( Mitchell et al. 2005).

Discussion.

Brown (1931) recognized the entity we here delimit as S. caumii as two varieties of S. nelsonii , a coastal species found on many islands in the Hawaiian archipelago. St. John (1988) placed S. nelsonii var. acuminatum in synonymy with S. nelsonii var. caumii . Solanum caumii is most similar to S. nelsonii but it can be distinguished by its semi-erect habit, larger leaf length to width ratio, and sometimes red fruit. In 2008, plants of S. nelsonii s.s. from Molokai were cultivated alongside individuals from Nihoa ( S. caumii ) in greenhouses at the New York Botanical Garden (made available through the conservation program at the National Tropical Botanical Garden in Honolulu by Drs. David and Lida Burney and their staff). Under identical growing conditions plants here recognized as S. caumii and S. nelsonii s.s. maintained their distinct forms.

Endemism on the small island of Nihoa is relatively common, it is only one of four of the outer Hawaiian islands that still has exposed basalt substrate. There are other species of endemic or near-endemic plants ( Amaranthus brownii Christoph. & Caum, Amaranthaceae ; Pritchardia remota Becc., Arecaceae ; Scheidea verticillata F.Br., Caryophyllaceae ) and the entire island has been designated critical habitat for them ( Mitchell et al. 2005). The island also hosts two endemic birds, at least seventeen endemic arthropods, and six endemic land snails ( Mitchell et al. 2005).

Additional specimens examined.

United States of America. Hawaii. Nihoa: sin. loc., 13 Jun 1923 (fl), Bryan 3 (BISH); Miller Valley, 22 Apr 1983 (fl), Conant 102 (BISH); base of Miller Valley, ca. 30 ft, 26 Aug 1968 (fl), Herbst 1210 (BISH, US); Middle Valley, ca. 500 ft, 27 Jul 1980 (fl, fr), Herbst & Takeuchi 6544 (US); East Palm Valley, ca. 300 ft, 27 Jul 1980 (fl, fr), Herbst & Takeuchi 6555 (BISH; US); (fr), Judd s.n. (K); Rocky Gulch, 100 m, 20 Jun 1923 (fr), Judd 6 (BISH); Rocky Gulch, 100 m, 20 Jun 1923 (fr), Judd 7 (BISH); Rocky Gulch, 100 m, 20 Jun 1923 (fl), Judd 8 (BISH); lower slopes above the east cove, 23 Sep 1964 (fl), Long 2424 (US); top of Miller’s Peak in crevice at top of “Devil’s Slide", north side of peak, 24 Sep 1964 (fl), Long 2434 (US); lower slopes west valley near water-course, ca. 350 ft, 24 Sep 1964 (fl), Long 2439 (US); near helicopter landing, 6 Mar 1964 (fl, fr), Munro s.n. (BISH); Kawaewae, 75 ft, 12 Aug 1947 (fl), St. John 22731 (K, PTBG, RSA, US); Papahanaumokuakea Marine National Monument, above Miller Valley W facing Miller Ridge, 76 m (fl, fr), 7 Apr 2006 Tangalin 717 (US); Papahanaumokuakea Marine National Monument, lower Miller Valley just above sea shelf, near National Wildlife Refuge sign and base camp, 12 m, 7 Apr 2006 (fl), Tangalin 722 (US).

Figures

Figure 4. Solanum caumii (F. Br.) D. McClelland (holotype of S. nelsonii var. caumii F. Br., E. Caum 84 BISH [acc. 581193, barcode BISH 1014622]). Reproduced with permission.

Figure 5. Distribution of Solanum caumii.