Solanum caatingae S.Knapp & Saerkinen, 2018

Knapp, Sandra & Saerkinen, Tiina, 2018, A new black nightshade (Morelloid clade, Solanum, Solanaceae) from the caatinga biome of north-eastern Brazil with a key to Brazilian morelloids, PhytoKeys 108, pp. 1-12 : 3-6

Solanum caatingae S.Knapp & Saerkinen sp. nov. Figure 1

Diagnosis.

Like Solanum americanum Mill., but differing in its glandular pubescence on all vegetative parts, larger flowers with longer anthers, glabrous adaxial calyx lobe surfaces and spreading to appressed calyx lobes in fruit.

Type.

Brazil. Bahia: Mun. Maracajú, Lagoa Itaparica 10 km W of São Inacio-Xique-Xique road at the turning 13.1 km N of São Inacio, 300-400 m alt., 26 Feb 1977, R.M. Harley [with S.J. Mayo, R.M. Storr & T.S. Santos] 19125 (holotype: RB [RB00464327, acc. # 271981]; isotype: CEPEC [acc. # 19367]).

Description.

Perennial herb, 0.4-1 m tall, perhaps occasionally annual or only persisting for a few years. Stems terete or slightly angled, lacking spinescent processes; young stems densely to sparsely pubescent with spreading glandular, simple uniseriate trichomes 0.5-1 mm long, the trichomes 4-15 celled, drying translucent; new growth densely glandular pubescent; bark of older stems greenish-brown or pale tan. Sympodial units unifoliate or difoliate, the leaves not geminate. Leaves simple, shallowly toothed, 2.5-10 cm long, 1-4.5 cm wide, ovate to broadly elliptic, widest in the lower half, membranous; adaxial and abaxial surfaces evenly glandular-pubescent with simple uniseriate trichomes to 2 mm long, these denser abaxially and along the veins, densely pubescent with minute glandular papillae on both leaf surfaces especially in young leaves; principal veins 4-6 pairs, drying paler than the lamina; base truncate and then abruptly attenuate on to the distal part of the petiole; margins shallowly and irregularly toothed, the teeth ca. 0.5 mm long, rounded at the tips and broadly deltate to semi-circular in outline; apex acuminate, the tip blunt; petiole (0.5) 1-2 cm, only winged from the attenuate leaf base in the distal half to third. Inflorescences internodal, 2-3.5 cm long, subumbelliform with most flowers in the distal portion or spaced ca. 0.5 mm apart, unbranched or furcate, with 5-8 flowers, densely and finely glandular-pubescent like the stems and leaves; peduncle 1.8-3 cm long; pedicels 0.7-0.8 cm long at anthesis, ca. 0.5 mm in diameter at the base, ca. 0.7 mm in diameter at the apex, slender and tapering, densely glandular-pubescent with short uniseriate trichomes and glandular papillae, spreading at anthesis, articulated at the base but the articulation point somewhat swollen and a minute stump that is darker in colour left on the rhachis, this especially visible in fruiting material; pedicels scars closely packed in the distal part of the inflorescence to 0.5 mm apart, with the lowermost ca. 1 mm distant from the rest. Buds globose to broadly ellipsoid, the corolla strongly exserted from the calyx tube before anthesis. Flowers 5-merous, all perfect. Calyx tube 1-1.5 mm long, conical to broadly conical, the lobes 1-1.5 mm long, ca. 1 mm wide, deltate and spathulate, densely glandular-pubescent like the pedicels with uniseriate trichomes and papillae, the tips rounded. Corolla 0.6-0.9 cm in diameter, white with a darker (green?) central star, stellate, lobed 2/3-3/4 of the way to the base, the lobes 2.5-3.5 mm long, 1.5-3 mm wide, triangular, reflexed to spreading at anthesis, the abaxial surfaces glabrous to sparsely papillate with a few glandular trichomes ca. 0.2 mm long. Stamens equal; filament tube minute; free portion of the filaments 0.5-1 mm long, glabrous or sparsely pubescent with a few weak tangled simple uniseriate trichomes adaxially at the very base; anthers 1.8-2.2 mm long, 0.7-1 mm wide, ellipsoid, bright yellow, smooth, poricidal at the tips, the pores elongating to slits with age. Ovary conical, glabrous; style 3.5-4 mm long, sparsely glandular pubescent with weak tangled trichomes and papillae in the basal half where included in the anther cone; stigma minutely capitate, densely papillate, not markedly different from the style. Fruit a globose berry, 0.7-1 cm in diameter, green when young, maturing shiny black; the pericarp thin but not translucent when dry (drying black); fruiting pedicels 0.9-1.2 mm long, tapering from a base ca. 1 mm in diameter to an apex 1-1.2 mm in diameter, not distinctly woody, spreading and becoming deflexed at fruit maturity, remaining on inflorescence; fruiting calyx not accrescent, the tube 1-1.5 mm long, the lobes 2-2.5 mm long, spreading and later reflexed, covering the lower ca. 1/4 of the berry, the abaxial surfaces not densely papillate (different to S. americanum where the surfaces are densely papillate). Seeds (30)50-80 per berry, 1-1.5 mm long, 1-1.2 mm wide, tear-drop shaped with a subapical hilum, reddish-gold, the surfaces minutely pitted, the testal cells pentagonal. Stone cells absent. Chromosome number: Not known.

Distribution

(Figure 2 ). Solanum caatingae is endemic to Brazil; widely scattered collections are known from the states of Bahia, Ceará, Paraiba and Goiás.

Ecology and habitat.

Solanum caatingae grows in dry formations known as “caatinga” or "savana estépica” ( Eiten 1983; Prado 2003), between 300 and 400 m elevation. The caatinga (from the Tupi language words “caa” forest and “tinga” white) formation is a xerophytic thorn scrub/forest with marked differences in rainfall between wet and dry seasons. The biome occurs within the Caatinga Biogeographic Domain ( IBGE 2004) in north-eastern Brazil. The Caatinga Domain is a complex mosaic of many biomes, ranging from the thorn forests of the caatinga proper (see Andrade-Lima 1981) to gallery forest, to humid forests on higher elevations ("brejos de altitude") and cerrado savannas ( Andrade-Lima 1981; Lleras 1997). Like many other morelloid species, S. caatingae apparently grows in somewhat disturbed and moist areas within the broader more xerophytic habitat and details of its ecological preferences will remain somewhat unclear until more field observations and collections can be made. All specimens seen were in both flower and fruit, so it is likely to flower and fruit all year round or at least when water is available.

Etymology.

The species epithet is a genitive noun and comes from the caatinga vegetation formation (e.g. Olson et al. 2000; IBGE 2004) from where most of the collections of this species are known.

Preliminary conservation status

( IUCN 2017). DD (Data Deficient; EOO=55,971 km2 [LC]; AOO=16 km2 [EN]). The paucity of collections of S. caatingae means we cannot assign a preliminary conservation status with any certainty. The widely scattered nature of collections, coupled with the extreme threats to caatinga vegetation, mean that the species is possibly of conservation concern, despite its relatively large EOO. More collections may be hiding in the many sheets of the widespread and common S. americanum held in Brazilian herbaria and we hope that the description of this taxon will stimulate its future discovery both in the field and in herbaria.

Discussion.

Solanum caatingae is morphologically most similar to the widespread circumtropical weed S. americanum . It differs from it most strikingly in its spread ing glandular pubescence of translucent trichomes (versus appressed eglandular pubescence of white trichomes) and longer anthers (ca. 2 mm long versus ca. 1.5 mm long). Several other glandular pubescent species of herbaceous solanums occur in the dry forests of South America, but these are mostly from the Chaco biome and do not overlap in distribution with S. caatingae (see Särkinen and Knapp 2016). Solanum caatingae can, however, be distinguished from these species (e.g. S. michaelis Särkinen & S.Knapp, S. nitidibaccatum Bitter, S. physalifolium Rusby, S. sarrachoides Sendtn., S. tweedianum Hook. and S. woodii Särkinen & S.Knapp) by its calyx that is not accrescent in fruit with the lobes spreading or slightly reflexed and its shiny black berries with no stone cells. Solanum arenicola Särkinen & P. Gonzáles is another glandular pubescent species with which S. caatingae could potentially be confused, but that taxon is Amazonian and occurs along rivers in the tropical rainforest; it has not yet been recorded for Brazil, but we expect it to occur in the western part of the country along the border with Bolivia and Peru. Morphologically, S. arenicola differs from S. caatingae in its larger flowers (8-12 mm in diameter versus 6-9 mm in diameter in S. caatingae ), longer anthers (3-4 x 0.8-0.9 mm versus 1.8-2.2 x 0.7-1 mm), smaller berry (3.5-7 mm versus 7-10 mm in diameter) and presence of stone cells in the berries.

Several species of European and African polyploid morelloids (e.g. S. nigrum L., S. retroflexum Dunal, S. villosum Mill.) are polymorphic for presence or absence of glandular trichomes and their occurrence does not correlate with relationships based on phenetic studies with molecular markers ( Manoko 2007; see Särkinen et al. 2018 for a discussion). In the Americas, however, glandular pubescence is correlated with other characters such as anther length and stone cell presence or absence, suggesting it can be of taxonomic significance.

The type collection (Harley et al. 19125) comes from near the edge of the Caatinga Biogeographic Domain as defined by the Instituto Brasileiro de Geografia e Estatística ( IBGE 2004) in a highly heterogeneous mosaic of caatinga and cerrado around a seasonal lake (Lagoa Itaparica) with stands of carnaúba palm ( Copernicia prunifera [Mill.] H.Moore, Arecaceae ). The plant itself was found near abandoned houses in a weedy area with Waltheria rotundifolia Schrank ( Malvaceae ), Sida spinosa L. ( Malvaceae ) and Calotropis procera (Aiton) W.T.Aiton ( Apocynaceae ) (R. Harley, in litt., 31 May 2018, extract from field diary dated 26 Feb 1977), suggesting that, like many other morelloid species, S. caatingae grows in disturbed sites with at least some moisture, perhaps accounting for its sparse distribution across its range. A duplicate of Harley’s collection was not found in the herbarium at Kew. The specimen collected by Johann Pohl at "Rio Maranhao" was collected between 1817 and 1821 and is from a small tributary of the Rio Tocantins slightly to the north of the Distrito Federal. This is at the very southern edge of the Caatinga Domain and is one of the priority areas for both conservation and study ( Tabarelli and Cardoso da Silva 2003).

Specimens examined

(paratypes). BRAZIL. Ceará: Mun. Lavras de Mangabeira, area a ca. 12 km a N do Distrito de Felixardo, 299 m, 24 Jul 2014, A. Costa-Lima et al. 1406 (HUEFS, RB). Goiás: Rio Maranhão, sin.dat., J.B.E. Pohl 2393 (W). Paraiba: Mun. Carrapateira, Sitio Volta, nos arredores do Açude Volta, 404 m, 24 Sep 2014, A. Costa-Lima et al. 1862 (HUEFS, RB).

Figures

Figure 1. Photograph of the holotype of Solanum caatingae (Harley et al. 19125, RB). Image courtesy of the Jardim Botanico do Rio de Janeiro (JBRJ).

Figure 2. Distribution of Solanum caatingae. Hatched area indicates the Caatinga Biogeographic Domain (sensu IBGE 2004).