Solanum hydroides Gouvea & Giacomin
Creators: name: Knapp, Sandra
name: Gouvêa, Yuri F.
name: Giacomin, Leandro L.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Solanales
Solanaceae
Solanum
Solanum hydroides

description: 3.Solanum hydroidesGouvêa & Giacomin, PhytoKeys 139: 66. 2020.
Fig. 7
Type.
Brazil. Minas Gerais: Mun. Teófilo Otoni, afloramento rochoso lado esquerdo da MG 418, cerca de 30 km norte de Teófilo Otoni, 560 m alt., 17°51'22"S, 41°15'39"W, 27 Jan 2014, L. F. A. de Paula, L. Azevedo, R. Fernandes & J. R. Stehmann 669 (holotype: BHCB [BHCB 053358]; isotype: RB [RB 01472905]).
Description.
Shrubs 1–1.5 m tall, erect, armed. Stems terete, directed upwards and spreading, moderately to densely pubescent and sparsely to moderately prickly, the trichomes eglandular, porrect-stellate, variably short- to long-stalked, the stalks 0.5–1.5 mm long, the rays 4–8, 0.5–1 mm long, the mid-points 1 – to 2 – celled, always shorter than the rays, the prickles 4–6 mm long, 2–6 mm wide at the base, broad-based and recurved; new growth densely stellate pubescent and sparsely prickly, the trichomes pale yellow to dark brownish-red; bark of older stems glabrescent, drying greenish-brown to dark brown. Sympodial units plurifoliate, the leaves not geminate. Leaves simple, nearly entire to shallowly lobed; blades 2.8–12.1 (21.8) cm long, 2.2–7.5 (10.1) cm wide, ca. 1.2 to 2 times as long as wide, elliptic to ovate, membranous, slightly discolorous, both surfaces prickly along the mid-rib and veins; adaxial surface densely to moderately stellate-pubescent and prickly, brown to dark green when dry, the trichomes like those of the stem, but with (1 –) 4–6 rays, the prickles along the mid-rib and major veins to 5.5 mm long and 1 mm wide at the base, straight and laterally compressed; abaxial surface more densely stellate-pubescent than the adaxial surface, whitish-green when dry, the trichomes like those of the adaxial surface, the prickles like those of the adaxial surface, but to 6.5 mm long and 2 mm wide at the base; base attenuate to truncate or rounded, less often with 1 or 2 basiscopic lobes, decurrent on to the petiole, sometimes asymmetrical; margins shallowly lobed, the lobes (0) 3–5 on each side, 1–12 (14.8) mm long, 3.2–11 (23) mm wide at base with usually acute, sometimes rounded or obtuse apices, the sinuses 3.2–8.5 mm deep; apex acute to acuminate; principal veins 4–6 pairs, more prominent beneath, prickly on both surfaces, the prickles 5–6 mm long, straight; petioles 0.6–3.3 cm long, densely to moderately pubescent with porrect-stellate trichomes like those of the leaves, usually armed with 1–5 prickles. Inflorescence internodal, to 6 cm long, unbranched, with 4–10 flowers, up to 2 flowers open at a time; axes glabrescent to densely pubescent, usually unarmed, the stellate trichomes like those of the stem, but these sometimes with the mid-point as long as the rays; peduncles 0.4–2.3 (- 3.8) cm long; pedicels 3–17 mm long, 0.5–0.8 mm in diameter at the base, to 1.5 mm in diameter at the apex, spreading to slightly deflexed, pubescent with trichomes like those of the inflorescence axes, unarmed, articulated at the base; pedicel scars evenly spaced 1–7 mm apart. Buds ovoid to ellipsoid, with the corolla enclosed in the calyx until just before anthesis. Flowers 5 - merous, heterostylous with long-styled flowers (co-sexual) at the base of inflorescence, short-styled (functionally staminate) flowers more distally, the plants andromonoecious. Calyx with the tube 2.6–4.3 (6) mm long, 6.5–8 mm in diameter, broadly obconical to cupuliform, the lobes 3–7 mm long, 3–5.5 mm wide, triangular to deltate, with acute to acuminate apices, glabrous adaxially, densely pubescent abaxially with bristly purple-tinged, hyaline or reddish-brown porrect to multangulate long-stalked stellate trichomes, the stalks 1.1–3.8 mm long, rays 4–8, to 1.5 mm long, the mid-points 1–2 celled, shorter than or the same length as the rays, armed or unarmed, if present, the prickles 2.8–4 mm long, 0.5–1 mm in diameter at the base, straight, acicular. Corolla 2.4–3 cm in diameter, white, often with a greenish-yellow star at the base, shallowly stellate, lobed ca. halfway to the base, interpetalar tissue nearly absent, the lobes 5.9–8.8 mm long, 9.9–12.2 mm wide, pubescent abaxially on the petal mid-vein and / or apices with sparse delicate short-stalked porrect-stellate trichomes with stalks to 0.9 mm long, the apices acute to apiculate. Stamens equal; filament tube to 1 mm long; free portion of the filaments 0.7–1 mm long, glabrous; anthers 6.5–8 mm long, 2.5–3 mm wide, broadly lanceolate and tapering, connivent or slightly divergent at the tips, glabrous, yellow, abaxially swollen in the lower half (gibbous) and somewhat papillate, poricidal at the tips, the pores directed distally, slightly extrorse, not lengthening to slits with age. Ovary somewhat conical, glabrous; style 8–10 mm long in long-styled flowers, ca. 3 mm long in short-styled flowers, straight, glabrous; stigma clavate to bilobed, the surface papillose and irregular, the style and stigma poorly developed in short-styled flowers. Fruit a globose berry, 0.9–1.8 cm in diameter, green to whitish-green at maturity, drying dark brown, glabrous, the pericarp matte; fruiting pedicels 1–1.5 cm long, 1–2 mm in diameter at the base, usually unarmed, deflexed from the weight of the fruit; fruiting calyx partially accrescent, the tube tightly investing 1 / 2–3 / 4 of the fruit at maturity, the lobes 5.8–8 mm long, 7–9.6 mm wide, not overlapping, pubescent with long-stalked porrect-stellate trichomes often with the base of the stalks markedly expanded and bristly, the stalks to 4.8 mm long. Seeds ca. 250 per berry, 2.2–2.6 mm long, 1.6–2 mm wide, pyriform to reniform, not markedly flattened, the surface irregularly pitted, the testal cells pentagonal in outline; stone cells absent. Chromosome number not known.
Distribution
(Fig. 8). Solanum hydroides is endemic to the south-eastern region of Brazil, with records in four localities in north-eastern Minas Gerais (Mun. Teófilo Otoni and Conselheiro Pena) and northern (Mun. Nova Venécia) and central (Mun. Santa Teresa) Espírito Santo States.
Ecology and habitat.
Solanum hydroides grows at the edge of seasonal semi-deciduous tropical rainforests associated with granitic or gneissic rock outcrops (inselbergs) and somewhat disturbed sites at their bases, such as roadsides and clearings; from 300 to 600 m elevation. It also occasionally grows in epilithic vegetation patches lying on the flatter parts of inselbergs.
Common names and uses.
None recorded.
Preliminary conservation status
(IUCN 2020). EOO (12,549 km 2, VU); AOO (24 km 2, EN). Solanum hydroides is known from only four disjunct localities in vegetation remnants associated with inselbergs: these rock outcrops harbour the last remnants of forest fragments (Martinelli 2007) in areas where they occur. Only one of these localities is within a protected area (APA Pedra do Elefante, Espiríto Santo State). Although we have seen a few more collections than were used in the original assessment (Gouvêa et al. 2020), we concur with their evaluation of S. hydroides as Endangered (B 2 a, b ii, iii, iv).
Discussion.
Solanum hydroides is a comparatively smaller plant than other species of the group, except S. sublentum; its smaller leaves and thinner stems, petioles and inflorescence axes give it a more delicate overall aspect. Solanum hydroides can, however, be readily distinguished from S. sublentum by its pubescence of stellate eglandular trichomes (Fig. 7 A, B) and by the widely obconical to cupuliform shape of the calyx at anthesis. In S. sublentum, the indumentum is of both conspicuous simple glandular trichomes and stellate eglandular trichomes (Fig. 13 E – G), with the stellate trichomes usually much less numerous than the simple ones and often early deciduous (i. e. present only in new growth). Calyces of S. sublentum are somewhat urceolate, inflated and prominently plicate at the top of the calyx tube (Fig. 13 J), whereas, in S. hydroides, calyces are tightly adherent to the berry at maturity and not notably plicate, especially in live plants.
Although being a markedly less robust plant, S. hydroides can be very similar to some specimens of S. hexandrum, the most variable species in the clade, with which it shares the indumentum of few-rayed stellate eglandular trichomes on the stems, leaves, inflorescence axis and calyces. Solanum hydroides differs from S. hexandrum in its white and smaller corollas (13–21.5 mm total length), shorter corolla lobes (5.9–8.8 mm long; Fig. 7 D) and accrescent, but not inflated, fruiting calyces that only partially cover the mature fruit (Fig. 7 E). Solanum hexandrum has corollas in various shades of lilac to purple and are larger (24.3–40 mm long), with longer corolla lobes (12.6–25 mm long; Figs 4 G, H, 5 G, H, I) and the fruiting calyces are accrescent and inflated, completely enclosing the mature fruit (Figs 4 J, 5 J). The corollas of S. hydroides are thin and membranous and easily tear apart between the lobes during the drying process, which can make the lobes on herbarium specimens seem longer than they really are. Care is needed to ensure correct measurements from herbarium specimens.
Leaf measurements are also useful for distinguishing S. hydroides from S. hexandrum. The leaves of S. hydroides are usually smaller (7.5–13.6 cm long and 5–8.7 cm wide) than those of S. hexandrum (17–45 cm long and 10.5–32 cm wide). Nevertheless, leaves of S. hydroides are larger in plants growing in shade and in young individuals (see Roe (1966) for other examples in Solanum) and we have seen plants with leaves to 22 cm long and 11 cm wide. Specimens of S. hydroides growing in shade are less densely pubescent, with less robust (i. e. stalks with fewer series of cells) and slightly shorter trichomes on stems, leaves and calyx. Corollas of these shade plants are usually larger in relation to the other flower parts (e. g. stamens and calyx).
Trichome morphology in S. hydroides is not particularly variable within individual plants and amongst plants of the same population; however, there is a significant variation in the number of trichome rays between some populations, as is seen also in S. hexandrum. Trichomes of specimens from the southernmost-known population (in Santa Teresa Municipality, Espirito Santo State) are mostly 6 - to 8 - rayed and usually denser, whereas those of plants from the other populations (Teófilo Otoni and Nova Venécia Municipalities of Minas Gerais State) are mostly 4 - rayed. Within individual plants, the variation in trichome morphology is limited to a reduction in the number of rays and is especially evident in plants with four-rayed trichomes. In these plants, the trichomes may lack one to almost all rays, sometimes with only the mid-point or a lateral ray remaining and the trichome appearing to be unbranched, but with a basal multiseriate stalk, as is also seen more dramatically in S. hexandrum. This kind of variation has been reported in other Solanum groups, such as the Brevantherum clade or members of the Acanthophora clade (Nee 1991; Levin et al. 2005; Stern et al. 2013).
description: Published as part of Knapp, Sandra, Gouvêa, Yuri F. & Giacomin, Leandro L., 2025, A revision of the endemic Brazilian Solanum hexandrum group (Leptostemonum, Solanum, Solanaceae), pp. 199-259 in PhytoKeys 253 on pages 199-259, DOI: 10.3897/phytokeys.253.138216