Solanum, sensu Stern et al. (2011) and Wahlert et al. (2014)

Knapp, Sandra, Sagona, Eva, Carbonell, Anna K. Z. & Chiarini, Franco, 2017, A revision of the Solanum elaeagnifolium clade (Elaeagnifolium clade; subgenus Leptostemonum, Solanaceae), PhytoKeys 84, pp. 1-104 : 7

The Elaeagnifolium clade of Solanum, sensu Stern et al. (2011) and Wahlert et al. (2014)

Solanum section Leprophora Dunal, Hist. Solanum 125, 181. 1813. Type species. S. elaeagnifolium Cav.

Solanum ellipticum species group sensu Whalen (1989), S. elaeagnifolium only, excl. type.

Solanum vespertilio group sensu Whalen (1989), S. houstonii only [as S. tridynamum ], excl. type.

Solanum section Lathyrocarpum G.Don, Series 2 Nee (1999), S. mortonii Hunz. only, excl. type.

Solanum section Lathyrocarpum G.Don, Series 4 Nee (1999). Type species: S. elaeagnifolium Cav. (incl. also S. hindsianum , S. houstonii [as S. tridynamum ]).

Description.

Shrubs, sometimes rhizomatous, armed or unarmed. Stems terete, pubescent with multangulate, porrect-stellate or lepidote trichomes, sometimes glabrescent. Sympodial units difoliate or occasionally trifoliate or plurifoliate, not geminate. Leaves simple to shallowly lobed to occasionally somewhat pinnatifid, concolorous or discolorous, densely pubescent with multangulate, stellate or lepidote trichomes; petioles well developed, sometimes channelled above. Inflorescences terminal to lateral, usually unbranched, occasionally furcate, not bracteate, with up to 10 flowers (exceptionally to 26 flowers in S. houstonii ), in andromonoecious plants with a single (or two) hermaphroditic long-styled flowers at the base and all distal flowers short-styled and functionally staminate; peduncle robust, clearly distinct armed or unarmed; pedicels articulated at the base, armed or unarmed. Flowers 5-merous, actinomorphic to zygomorphic, perfect or strongly heteromorphic with long- and short-styled morphs and the plants andromonoecious. Calyx armed or unarmed, the lobes deltate and usually strongly keeled with an elongate acumen. Corolla stellate or rotate stellate, purple or occasionally white, usually with a green star at the base, the lobes spreading or slightly reflexed at anthesis. Stamens unequal, sometimes markedly so ( S. houstonii ), the filaments equal, the anthers strongly tapering with distally directed pores, usually somewhat spreading and not connivent. Ovary conical, vestigial in strongly andromonoecious species, glabrous or sparsely stellate-pubescent; style in long-styled flowers straight or curved, glabrous or sparsely stellate-pubescent near the base; stigma clavate in long-styled flowers, vestigial in short-styled flowers. Fruit a globose berry, indehiscent or dehiscent, often enclosed in the accrescent calyx; pericarp brittle at fruit maturity, glabrous. Seeds flattened reniform, yellowish tan or blackish brown, often shiny with what appears to be a sticky substance. Chromosome number: n=12, 24, 36 ( Moscone 1992; Acosta et al. 2005; Scaldaferro et al. 2012; Chiarini et al. in press).

Distribution.

An exclusively New World group occurring in North America (western United States and Mexico) and southern South America (Argentina, Paraguay, Brazil, Uruguay, Chile). One species, S. elaeagnifolium , is an invasive weed in dry areas worldwide.

Discussion.

As discussed above under Phylogeny and as can be seen by the synonymy of the clade, members of this group were previously not thought to be closely related. Their resolution as sister to the diverse and diversifying Old World clade of spiny solanums makes them of particular interest in terms of character evolution. Nee (1999) placed all of the species treated here in his section Lathyrocarpum (whose type species is S. carolinense L., see Wahlert et al. 2015) in two different series; in this he followed the views of Hunziker (1979).

The clade, as is common with the groups of spiny solanums, has few unambiguous and unique synapomorphies. The andromonoecious habit (very weak in S. elaeagnifolium ), unusual dry and often dehiscent berries, dark sticky seeds, silvery pubescence and propensity to grow in arid zones are all characters that are shared by the species in this group. None of these are unique to the S. elaeagnifolium group, however, either in Solanum or in Solanaceae more widely, although the dehiscent berries of all these species (save S. elaeagnifolium ) are only rarely found in Solanum (e.g., S. tununduggae , S. vansittartensis of Australia, see Symon 1981; Knapp 2002a).

Artificial key to the species of the S. elaeagnifolium group

1	Pubescence of leaves lepidote, the trichomes with the rays fused at the base; prickles, if present, often orange; flowers mostly all perfect; stamens equal or nearly so; fruits more than 1 per infructescence	1. Solanum elaeagnifolium
-	Pubescence of leaves stellate or multangulate, the trichomes with the rays not fused or if very slightly fused near the base; prickles, if present, brown or yellow; flowers heteromorphic, not all perfect; stamens unequal; fruits usually 1 per infructescence.	2
2	Trichomes of stems and leaves multangulate, the rays in multiple planes; Argentina	5. Solanum mortonii
-	Trichomes of stems and leaves stellate, the rays in a single spreading plane (porrect-stellate)	3
3	Pedicels strongly deflexed in fruit; trichome rays always fewer than 10; midpoint equal in length to the lateral rays; flowers white; Argentina	3. Solanum homalospermum
-	Pedicels erect in fruit; trichome rays usually more than 10; midpoint shorter than the lateral rays; flowers purple or lavender (occasionally white); Mexico	4
4	Flowers weakly heteromorphic, the anthers in hermaphroditic and staminate flowers not different, straight or only slightly curved; fruiting calyx not or only sparsely prickly, usually not covering the berry by more than 2/3 of its length; Sonoran Desert	2. Solanum hindsianum
-	Flowers strongly heteromorphic, the hermaphroditic flower with the anthers more or less equal in size, the staminate flowers with 3 anthers much longer than the rest and strongly curved; fruiting calyx prickly, accrescent and almost completely enclosing the berry; widespread in Mexico	4. Solanum houstonii