Tradescantia atlantica M.Pell., 2018

Pellegrini, Marco O. O., 2018, Wandering throughout South America: Taxonomic revision of Tradescantia subg. Austrotradescantia (D. R. Hunt) M. Pell. (Commelinaceae), PhytoKeys 101, pp. 1-97 : 12

1. Tradescantia atlantica M.Pell. sp. nov. Figs 8 , 9

Diagnosis.

Similar to T. tenella due to its definite base, erect and densely branched stems, involute ptyxis, leaf-blades with conspicuous secondary veins, saccate and strongly unequal cincinni bracts, keeled sepals, pistil the same length as the stamens, seeds with rugose testa and hilum shorter than ½ the length of the seed. It can be differentiated by its fibrous stems, sessile leaves with velutine to hispid, light brown to hyaline indumentum, broadly ovoid floral buds, sepals with a mixture of glandular and eglandular hairs restricted to the keel and petals always white and plicate.

Type.

BRAZIL. Rio de Janeiro: Nova Friburgo, Reserva Ecologica de Macae de Cima , fl., fr., 26 Jan 2012, M.O.O. Pellegrini et al. 207 (holotype: RB barcode RB01025675!) .

Description.

Herbs ca. 10-35 cm tall, with a definite base, terrestrial. Stems erect, fibrous, branched to densely branched; internodes 1.8-6.1 cm long at base, distally shorter, dark green to vinaceous, glabrous, except for a leaf-opposed longitudinal line of short, uniseriate, light brown to hyaline hairs. Leaves distichously-alternate, sessile; ptyxis involute; sheaths 4.1-7.6 mm long, light green to pink with dark green to purple striations, glabrous, margin setose, hairs light brown to hyaline; blades 3.3-10.2 × 0.9-3.4 cm, elliptic to ovate, flat, membranous to chartaceous, velutine to hispid on both sides, rarely hairs restricted to the midvein, hairs light brown to hyaline, adaxially dark green, abaxially green, sometimes with vinaceous blotches, turning dark brown to olive-green on both sides when dry, base obtuse to rounded, margin ciliolate, slightly revolute, apex acute to acuminate; midvein conspicuous, adaxially impressed, secondary veins conspicuous, adaxially impressed, abaxially prominent, becoming more evident on both sides when dry. Synflorescences terminal or axillar in the distal portion of the stems, composed of a solitary main florescence, 1 per leaf axis. Inflorescences (main florescences) consisting of a pedunculate double-cincinni fused back to back; peduncles 1.9-3.7 cm long, dark green to vinaceous, glabrous, except for a leaf-opposed longitudinal line of short, uniseriate, light brown to hyaline hairs; basal bract inconspicuous, tubular, hyaline, glabrous; peduncle bracts absent; supernumerary bracts absent; cincinni bracts 1.2-3.4 × 0.4-1.3 cm, leaf-like, unequal to strongly unequal to each other, elliptic to narrowly ovate to ovate, velutine to hispid on both sides, rarely hairs restricted to the midvein, hairs light brown to hyaline, adaxially dark green, abaxially green with vinaceous blotches, base cordate to round, saccate, margin ciliolate, slightly revolute, apex acuminate; double-cincinni (4-)6-8-flowered; bracteoles inconspicuous, imbricate, linear-triangular to triangular, hyaline. Flowers 1.1-1.3 cm diam.; floral buds broadly ovoid, apex acute; pedicels 1.2-3.4 mm long, upright at anthesis and pre-anthesis, reflexed at post-anthesis, vinaceous, densely glandular-pubescent, rarely with a mixture of glandular and eglandular, hyaline hairs; sepals 3.8-5.3 × 2.6-4.2 mm, dorsally keeled, with a mixture of glandular and eglandular, hyaline hairs restricted to the keel, hairs hyaline to light brown; petals 6.6-8.2 × 3.7-5.2 mm, plicate, white; filaments 3.6-4.9 mm long, anthers 0.4-0.6 × 0.5-0.6 mm; ovary 0.9-1.1 × 0.8-1.2 mm, style 3.8-4.0 cm long, pistil the same length as the stamens. Capsules 3-3.5 × 2.1-2.4 mm. Seeds 1.4-1.6 × 1.1-1.3 mm, greyish-brown to brown, not cleft towards the embryotega, rugose; hilum shorter than ½ the length of the seed.

Specimens seen (paratypes).

BRAZIL. Minas Gerais: Tiradentes, caminho para a Serra de São José, fl., fr., 16 Jan 1994, A.M. Giulietti et al. 13666 (K, SPF). Rio de Janeiro: Itatiaia, Parque Nacional do Itatiaia, Planalto, proximidades do Brejo da Lapa, fl., fr., 3 Dec 1996, J.M.A. Braga et al. 3708 (RB); Nova Friburgo, Furnas do Catete, fl., fr., 4 Apr 1965, J.C. Siqueira 2032 (FCAB); fl., fr., 3 Jun 1987, L.C. Giordano & D.P. Costa 313 (RB). São Paulo: São Paulo, Santo Amaro, Seminário Espírito Santo, fl., fr., 20 Oct 1943, L. Roth 812 (SP); Parque Estadual da Serra do Mar, margem esquerda do Rio Quilombo, fl., 9 Oct 1989, D.G. Scaravelli s.n. (ESA no. 5253, RB no. 628820); Tapiraí, Cachoeira do Chá, fl., 18 Oct 1994, K.D. Barreto et al. 3056 (ESA, RB, SPVR, US).

Distribution and habitat.

Tradescantia atlantica is endemic to Brazil, more precisely to the states of Minas Gerais, Rio de Janeiro and São Paulo; in the Atlantic Forest domain (Fig. 9 ). It can be found growing as a terrestrial understorey in shaded and moist forests.

Phenology.

It was found in bloom and fruit from October to June but peaking during January.

Etymology.

The epithet makes reference to this species’ distribution range, restricted to the Atlantic Forest domain.

Conservation status.

Tradescantia atlantica possesses a wide EOO (ca. 60,715.793 km2), but a considerably narrow AOO (ca. 32.000 km2). Since it is only known from seven very fragmented collections, following the IUCN (2001) recommendations, T. atlantica should be considered Endangered [EN, A2cde+B2ab(ii, iii, iv)+D2].

Comments.

Tradescantia atlantica is a member of the T. tenella species complex, being morphologically similar to T. tenella and T. tucumanensis , due to its definite base, conspicuous secondary veins (Fig. 8B ), saccate and unequal to strongly unequal cincinni bracts (Fig. 8F ), keeled sepals (Fig. 8G ), pistil the same length as the stamens (Fig. 8H ), seeds with rugose testa and hilum shorter than ½ the length of the seed (Fig. 8I ). It was previously tentatively included by me ( Pellegrini 2015) under a much broader T. tenella , due to its erect stems and ovoid floral buds. Nonetheless, after further herbarium and field studies, I have come to the conclusion it indeed merits taxonomic recognition. The fibrous stems and sessile leaves (Fig. 8B ) vegetatively differentiate T. atlantica from T. tenella , with the fibrous stems being unique in the subgenus. Also, the velutine to hispid indumentum covering the leaves (Fig. 8C ) is different from the much coarser indumentum observed in T. tenella (Fig. 2E ), while the indumentum in the sepals is composed of a mixture of glandular and eglandular hairs (Fig. 8G ), as opposed to the evenly glandular pubescent sepals of T. tenella (Fig. 2F ). Finally, the plicate petals of T. atlantica (Fig. 8H ) are only observed in the not so closely related T. fluminensis (Fig. 6E ) and the distribution of T. atlantica and T. tenella has no overlaps.

Tradescantia atlantica can also be differentiated from the new T. tucumanensis by its fibrous stems (vs. succulent in T. tucumanensis ), sessile leaves with velutine to hispid indumentum (vs. at least the basal ones subpetiolate, sparsely hirsute to hirsute), broadly ovoid floral buds (vs. ellipsoid), sepals with a mixture of glandular and eglandular hairs restricted to the keel (vs. with a mixture of glandular and eglandular hairs, but exclusively hispid along the keel in T. tucumanensis ) and petals always white and plicate (vs. ranging from white to pink and flat).

Figures

Figure 2. Indumentum morphology in Tradescantia subg. Austrotradescantia. A completely glabrous stems and leaves in T. seubertiana B glabrous leaf-blade of T. crassula, showing the ciliate margin C abaxial side of a leaf-blade of T. cerinthoides, showing the sparsely hispid indumentum D adaxial side of a leaf-blade of T. cerinthoides, showing the hispid indumentum E adaxial side of a leaf-blade of T. tenella, showing the hirsute indumentum and ciliate margin F sepal of T. tenella, showing the glandular-pubescent indumentum. Photos by M. O. O. Pellegrini.

Figure 6. Floral morphology in Tradescantia subg. Austrotradescantia. A-C floral buds A floral bud of T. cerinthoides, showing the vinaceous coloration, densely hispid indumentum and absence of dorsal keels in the sepals B floral bud of T. fluminensis, showing the medium green colouration and pilose eglandular hairs restricted to dorsal keels C floral bud of T. tenella, showing the green colouration, glandular-pubescent indumentum and the presence of dorsal keels in the sepals D-H flowers D front view of a flower of T. atlantica, showing the plicate petals E front view of a flower of T. fluminensis, showing the plicate petals F side view of two flowers of T. fluminensis, showing the plicate petals and the deflexed flowers at post-anthesis G front view of a flower of T. tenella, showing the flat petals H front view of a flower of T. umbraculifera, showing the flat and elliptic petals. Photos by M. O. O. Pellegrini.

Figure 8. Tradescantia atlantica M. Pell. A Estacao Ecologica de Macae de Cima, Nova Friburgo, state of Rio de Janeiro, Brazil B habit, showing the erect, fibrous and little branched stems C young shoot, showing the densely hispid indumentum D mature stem, showing the dark green to vinaceous and glabrous internodes with the leaf-opposed line of uniseriate hairs E-F inflorescence E overview of the inflorescence F detail of the main florescence, showing the unequal cincinni bracts G detail of the pedicels, showing the vinaceous colouration and glandular hairs H front view of a flower, showing the plicate petals I dorsal and ventral views of the seed, showing the rugose testa not cleft towards the embryotega and the hilum shorter than 1 / 2 the length of the seed. Photos by M. O. O. Pellegrini.

Figure 9. Distribution of Tradescantia atlantica M. Pell. Orange- Cerrado; Red- Caatinga; Dark green- Atlantic Forest.