Solanum hexandrum Vell.

Knapp, Sandra, Gouvêa, Yuri F. & Giacomin, Leandro L., 2025, A revision of the endemic Brazilian Solanum hexandrum group (Leptostemonum, Solanum, Solanaceae), PhytoKeys 253, pp. 199-259 : 199-259

2. Solanum hexandrum Vell. , Fl. Flumin. 88. 1829.

Figs 4 , 5

Solanum hexandrum Vell. var. minax Sendtn. , Fl. Bras. (Martius) 10: 71. 1846. Type. Brazil. São Paulo: “ primaevis sulvis supra Serra do Mar, Prov. Sebastianopolit. ”, Dec, C. F. P. van Martius s. n. (lectotype, designated here: M [M- 0171650]).

Solanum maroniense Poit. var. hexandrum (Vell.) Dunal , Prodr. [A. P. de Candolle] 13 (1): 319. 1852. Type. Based on Solanum hexandrum Vell.

Solanum echidniforme Dunal , Prodr. [A. P. de Candolle] 13 (1): 324. 1852, as " echidnaeforme ". Type. Brazil. Sin. loc., J. Lhotsky s. n. (holotype: G-DC [G 00131228]).

Solanum polytrichum Moric. var. enoplocalyx Dunal , Prodr. [A. P. de Candolle] 13 (1): 324. 1852. Type. Brazil. Rio de Janeiro: Serra dos Orgãos [“ circa de Rio de Janeiro ” – protologue], C. Gaudichaud 500 (lectotype, second step designated here; first step designated by Nee 1996, pg. 32 [as “ holotype ”]: P [P 00368655]; isolectotype: P [P 00368656]).

Solanum maroniense Poit. forma hexandrum (Vell.) Voss , Vilm. Ill. Blumengartn., ed. 3, 1: 719. 1894. Type: Based on Solanum hexandrum Vell.

Type.

Brazil. [Rio de Janeiro]: “habitat silvis nondum cultis”; (lectotype, designated by Knapp et al. (2015), pg. 831: [illustration] Original parchment plate of Flora Fluminensis in the Manuscript Section of the Biblioteca Nacional, Rio de Janeiro [cat. no.: mss 1198651_125] and later published in Vellozo, Fl. Flumin. 2: tab. 122. 1831).

Description.

Shrubs (0.5 -) 1–2.5 m tall, erect or occasionally somewhat spreading, strongly armed. Stems terete, glabrous to densely pubescent and / or bristly, sparsely to densely prickly, the stellate trichomes long-stalked, eglandular, porrect-stellate or less often appearing simple due to the complete lack of rays, the stalks 1–5 mm long, multiseriate, the rays 4–7, ca. 1 mm long, the mid-point ca. 0.5 mm long, always shorter than the lateral rays, with age the trichomes becoming thicker and the stems then densely bristly, the bristles often tipped with stalks and rays, underlying pubescence of minute papillate trichomes dense, more apparent on more glabrous individuals, the prickles 0.3–2 cm long, yellowish-golden, broad-based, the base 1.5–2 mm in diameter; new growth glabrous to densely stellate-pubescent and bristly, the multiseriate stalks of stellate trichomes usually shorter than the rays, but lengthening with leaf expansion; bark of older stems dark brownish-black in herbarium specimens, dark brown in live plants. Sympodial units unifoliate or difoliate, the leaves not geminate. Leaves simple or shallowly lobed (in some specimens, for example, de Paula 641, Giacomin 1827 deeply lobed) and repand, the blades 12–35 (- 40) cm long, 8–26 (- 30) cm wide, ca. 1.3–1.5 times as long as wide, broadly elliptic to narrowly obovate, usually widest in the basal half, membranous, concolorous, usually prickly on both surfaces with scattered straight prickles to 0.4–1.5 cm long, the prickles occasionally absent; adaxial surface glabrous to sparsely to moderately and evenly pubescent with long-stalked porrect-stellate trichomes, the stalks 1–1.5 mm long, multiseriate and arising from an expanded base, the rays 4–7, 1–2 mm long, the mid-point 0–1 mm long, always shorter than the rays, in some individuals, the rays often lost and the trichomes then appearing to be composed of a multiseriate base 1–1.5 mm long with a single celled tip often bent at 90 ° to the leaf surface; abaxial surfaces glabrous to evenly and densely pubescent with similar porrect-stellate long-stalked trichomes, but the stalks thinner and shorter than those on the adaxial surfaces and the rays occasionally more numerous, the trichomes denser along the veins, the surface densely dotted with crystal sand (inclusions of calcium oxalate, this not visible on the upper surfaces); principal veins 4–6 pairs, prickly or not, the prickles, if present, 0.4–1.5 cm long, on both surfaces; base attenuate on the petiole with a wing of ca. 2 mm wide along half the petiole length, sometimes to base of petiole; margins entire to 6 - lobed, the lobes usually shallow, the sinuses less than 1 / 4 of the distance to the mid-rib; apex acute to attenuate; petiole (0.1 -) 2–10 cm long, glabrous to densely stellate pubescent and bristly, usually sparsely prickly. Inflorescences opposite the leaves or internodal, (1.5 -) 2.5–6 (- 8) cm long, unbranched (rarely furcate), with 3–10 flowers; axes glabrous to densely stellate-pubescent and prickly like the rest of the plant, the bristles and trichomes grading into each other and not distinct in morphology; peduncle (0.5 -) 2–7 cm long; pedicels 1–2 cm long, 1–1.5 mm in diameter at the base, 1.5–2 mm at the apex (excluding trichomes), erect to spreading, glabrous to densely stellate-pubescent and bristly, if prickly, the prickles ca. 1 mm long and thinner than those of stems and leaves, articulated at the base; pedicel scars more or less evenly spaced 5–7 mm apart on mature inflorescences, more tightly packed distally. Buds globose to broadly elliptic, the corolla completely included in the saccate calyx tube until just before anthesis, the younger buds less bristly and prickly than older ones. Flowers 5–6 - merous, mostly co-sexual, but a few distal flowers are sometimes short-styled and probably functionally staminate. Calyx with the tube 4–7 mm long, 7–10 mm in diameter, cup-shaped and often completely closed in bud sometimes until just before anthesis, green or purple-tinged, the lobes 5–10 mm long, irregularly tearing at anthesis, but generally broadly triangular to deltate, acute to acuminate apically, glabrous to bristly and prickly with long-stalked bristles / trichomes, these with or lacking rays, the multiseriate stalk often purple-tinged. Corolla 3–6 cm in diameter, purple (rarely white), stellate, lobed halfway to the base, interpetalar tissue thin, glabrous, the lobes 15–21 mm long, 8–15 mm wide, deltate, spreading at anthesis, abaxially sparsely to densely pubescent with long-stalked porrect stellate trichomes, the stalks to 1 mm long, these denser at the tips and along the petal mid-vein, pubescence of corollas often purple-tinged, adaxially glabrous or with a few weak stellate trichomes on the mid-vein, the mid-veins often white adaxially. Stamens equal; filament tube minute to 0.5 mm long, glabrous; free portion of the filaments 1–1.5 mm long, glabrous; anthers (7 -) 9–11 cm long, 2–3 mm wide, broadly lanceolate and tapering, connivent, glabrous, yellow, abaxially swollen in the lower half (gibbous) and somewhat papillate, poricidal at the tips, the pores directed distally, not elongating to slits with age. Ovary conical, sparsely to densely pubescent with sessile stellate trichomes with rays 2–3 mm long, these soon deciduous; style 10–15 mm long in long-styled flowers (in rare short-styled flowers, the style 3.5–7 mm long), straight, glabrous; stigma clavate or broadly capitate, the surface minutely papillose. Fruit a globose to flattened globose berry, 2–2.5 (- 3.5) cm in diameter, green or pale whitish-green, glabrous, the pericarp somewhat shiny when dry, the berry almost completely enclosed in the accrescent saccate calyx; fruiting pedicels 1.8–2.3 cm long, 1.7–2.5 mm in diameter at the base, woody and spreading to somewhat deflexed from the weight of the fruit; fruiting calyx strongly accrescent, inflated or not, almost completely enclosing the berry, the tube 1.5–2 cm long, the lobes 1.5–2 cm long, irregular, usually overlapping, glabrous to sparsely to densely bristly and prickly with multiseriate bristles occasionally topped with porrect rays. Seeds ca. 100 per berry, 2–3.5 mm long, 1.5–2 mm wide, flattened reniform to somewhat ovoid, unwinged, reddish-brown or dark brown when dry, the surface minutely pitted, the testal cells pentagonal in outline, equal in size over the entire seed surface; stone cells absent. Chromosome number not known.

Distribution

(Fig. 6 ). Solanum hexandrum is endemic to the south-eastern region of Brazil and is known from the States of São Paulo, Rio de Janeiro, Minas Gerais, Espirito Santo and Bahia.

Ecology and habitat.

Solanum hexandrum grows in the wet forests of the Mata Atlântica, often in openings and along roads and streams; it occurs from almost sea level to 1,600 m elevation.

Common names and uses.

Brazil. Minas Gerais: juá-bravo (a widely used vernacular name for any spiny solanum in Brazil). No uses have been recorded.

Preliminary conservation status

( IUCN 2020). EOO (327,280 km 2, LC); AOO (460 km 2, EN). Solanum hexandrum is the most collected of any of these species and all forms of the variation are known from many localities, several of which are within protected areas (e. g. Parque Nacional da Serra dos Orgãos, Parque Nacional do Caparaó, Parque Estadual da Pedra Selada in Rio de Janeiro State; Parque Estadual da Serra do Brigadeiro in Minas Gerais State; RPPN Cafundó, Parque Estadual Mata das Flores in Espírito Santo State; RPPN Serra do Teimoso and RPPN Serra Bonita in Bahia State; Estação Ecológica de Bananal in São Paulo State). Nevertheless, given its high degree of variability that needs further study, we suggest it be assigned a preliminary status of Near Threatened based on criteria (B 2 a, b (ii, iii, iv).

Discussion.

Solanum hexandrum is the most variable species in the clade in terms of calyx and corolla shape and degree of pubescence, but is otherwise remarkably uniform. More glabrous individuals from the more northerly part of the species range have been called S. echidniforme Dunal , although the type of that species (G 00131228) is a sparsely bristly plant and fits within the overall circumscription as we treat this species here. The more glabrous individuals of S. hexandrum (mostly from the State of Espirito Santo) are strikingly different looking morphologically from more pubescent individuals (see Fig. 5 ), but there is a continuous gradation from glabrous to densely pubescent when specimens from across the range are examined. In several localities, individuals of both types are found and it is not clear if the differences are due to environmental or genetic factors.

The pubescence variability in S. hexandrum is extreme, with glabrous and pubescent individuals at first glance appearing to be completely different morphologically. Some other variation seems to be correlated with lack of rayed stellate trichomes; glabrous plants often have the calyx lobes fused until just before anthesis (see Fig. 5 B, D ), but this is not completely consistent (see Fig. 5 C ). The calyx in these glabrous plants is also often more saccate than in populations from elsewhere in the range (Fig. 5 J versus Fig. 4 J ), but this also varies and is difficult to assess on herbarium sheets when all reproductive stages are not present. The single specimen of S. hexandrum which we have seen with a branched inflorescence (Brotto et al. 3265, MBM) comes from amongst these glabrous plants.

The unusual stellate trichomes with the single-celled mid-point bent at an approximately 90 ° angle to the multiseriate base (see Fig. 5 L ) are found on the leaves in many populations of S. hexandrum , even if very sparsely. Leaf shape also varies across the range, with some populations from Rio de Janeiro having very narrow, more deeply lobed leaves (e. g. Giacomin 1827). The range of variation in trichome morphology in S. hexandrum warrants further study at a population and genetic level to determine if these variants represent distinct entities. Loss of prickles (derived from stellate trichomes) has been shown to be common across spiny solanums ( Satterlee et al. 2024) and it may be that the extremes seen in S. hexandrum could be genetically quite simple.

Solanum hexandrum was described and illustrated in the late 18 th century by Brother José Mariano Conceição da Vellozo (1742–1811) for his " Flora Fluminensis ". Vellozo was a parish priest in Rio De Janeiro and completed his work in 1790, but, unfortunately, this work was not published until long after he had died in 1811 ( Carauta 1969, 1973). The somewhat telegraphic descriptions of Solanum ( Vellozo 1829) referred to original illustrations now held in the library of the Biblioteca Nacional, Rio de Janeiro; printed illustrations, based on these originals, were published several years later ( Vellozo 1831). Typification of names of Solanaceae in Flora Fluminensis was treated by Knapp et al. (2015); the original illustration that is the lectotype for S. hexandrum is unambiguous and clearly shows the 6 - parted corolla that inspired the specific epithet.

Many herbarium specimens of S. hexandrum are annotated as S. maroniense Poit. , a species described only a year after ( Poiteau 1830). The description of S. maroniense is of a cultivated plant and is quite telegraphic, but is clearly stated to come from “ fleuve Maroni ” (the River Maroni) in French Guiana. Although, from the description alone, S. maroniense could correspond to S. hexandrum , the locality suggests it represents a plant of S. crinitum Lam. Solanum crinitum is common in the Guianas and a neotype will be selected as part of upcoming monographic work on the Crinitum clade.

Sendtner (1846) described a variety (“ β minax ”) citing a manuscript name of Martius, citing several specimens from various collectors, as well as plants from the garden in Munich. A sheet at Munich (M- 0171650) exactly matches the very precise locality information and date given in the protologue for a specimen collected by C. F. P. von Martius and we select this as the lectotype; it is the most unambiguous of the syntypes and appears to have been annotated by Sendtner. Another sheet at Munich (M- 0171847) has a description and the annotation “ Solanum minax ” in Martius’ hand is probably also a syntype; this sheet was collected in “ Oct ” while the lectotype was collected in “ Dec ” – the protologue states “ Octobri ad Decembrem florens ”. Other collections cited have no or less unambiguous localities (see Suppl. materials 1, 2). Sendtner (1846) suggested that S. latifolium Poir. (= S. rigidum Lam. ) might be a synonym of S. hexandrum ; this species is endemic to the Cape Verde Islands and related to the brinjal eggplant ( Knapp and Vorontsova 2013).

Dunal (1852: 324) cited Gaudichaud 501 from Rio de Janeiro in “ h. Mus. Paris ” in his circumscription of S. polytrichum Moric. var. longifolium along with Blanchet 602 from Bahia in “ h. DC ”. Solanum polytrichum var. longifolium is illegitimate and superfluous as he ( Dunal 1852: 324) cited an earlier name at the varietal level, S. polytrichum var. grandifolium Sendtn. ( Sendtner 1846) , in synonymy. The three specimens of Gaudichaud 501 in P (P 00368657, P 00368658, P 00368659) are of a plant of S. hexandrum and, although P 00368657 has been annotated as an “ Isosyntype of Solanum polytrichum Moric. var. longifolium Dunal ”, this collection has no status as a type. Both collections (Gaudichaud 500, 501) cited by Dunal (1852) may actually have been collected by Frederich Sellow (see Moraes (2023)).

Gaudichaud 500 in “ h. Mus. Paris ” was the only element cited in the protologue of S. polytrichum var. enoplocalyx ( Dunal 1852) . Nee (1996) cited as “ holotype ” Gaudichaud 500 in P and cited two photographs taken by C. V. Morton (Morton neg. 8300, 8301, both held in US). Two sheets of this collection are in P, one bears the original locality label (P 00368655), while the other (P 00368656) has an undated label in what appears to be Dunal’s hand. Both are scrappy specimens with tiny apical leaves, but P 00368655 has two inflorescences, one in flower and one in early fruit. As the more complete specimen, we select the sheet P 00368655 of Gaudichaud 500 as the second step lectotype for S. polytrichum var. enoplocalyx . This sheet is labelled as an isotype. Both of these sheets are very similar morphologically to those labelled Gaudichaud 501 and may have been collected together.

Figures

Figure 4. Solanum hexandrum (pubescent individuals) A habit B inflorescence C – E buds showing differences in colour and shape F open flower G long-styled flower with 6 lobes H short-styled flower with 5 lobes I developing fruits enclosed in purple-tinged calyx J mature berries with tightly appressed accrescent calyx (A, B Stehmann et al. 4513; C Giacomin et al. 875; D, G, I Agra et al. 7359; E, F, H Giacomin et al. 1827; J Gouvêa & Salino 514). Photos: A, B João R. Stehmann D, G, I Leandro L. Giacomin E, F, H Lynn Bohs J Yuri F. Gouvêa.

Figure 5. Solanum hexandrum (glabrous individuals) A habit at forest edge B inflorescence C – F buds showing variation in fusion of calyx during development G open long-styled flowers H open short-styled flower I open short-styled flowers showing corolla expansion (enlargement) during flowering J mature berry with calyx removed K upper leaf surface with prickles and no stellate trichomes L upper leaf surface with prickles and rayless stellate trichomes with bent mid-points M lower leaf surface with broad-based prickles along the veins (A, B, H Giacomin et al. 1833; C Giacomin et al. 1844; D, I, J Gouvêa & Falcão 137; E, L Gouvêa & Falcão 135; F Gouvêa & Stehmann 158; G, K, M Gouvêa & Stehmann 159). Photos: A, C Lynn Bohs B, H Leandro L. Giacomin D, E, I, J, L Yuri F. Gouvêa F, G, K, M João R. Stehmann.

Figure 6. Distribution of S. hexandrum.