Tibouchina rosanae P. J. F. Guim. & Woodgyer, 2016

Guimarães, Paulo José Fernandes & Woodgyer, Elizabeth M., 2016, A new and unusual amphistomatic species of Tibouchina (Melastomeae, Melastomataceae) from Brazil, Phytotaxa 246 (2), pp. 145-151 : 146-150

Tibouchina rosanae P. J. F. Guim. & Woodgyer , sp. nov. ( Figs. 1 and 2 ).

TYPE: ― BRAZIL. Mato Grosso: Santa Cruz do Xingu, Parque Estadual do Xingu , limite norte do parque, 9°45’22’’ S, 52°38’6’’ W, 289 m. 10 Mar 2011 (fl.), Soares , C. R. A .; Zappi, D. C .; Frisby, S .; Milliken, W .; Forte, A. F .; Silva, D. R. & Lindolfo, L. F. 3217 (holotype: RB!; isotypes: K!, UNEMAT, UPCB) .

Diagnosis: —This new species is similar to Tibouchina johnwurdackiana Todzia (1997: 537) because of its strigose leaf indumentum covered on both sides with linear trichomes adnate to the surface for most of their length. It differs by its habit as a branched shrub (vs. unbranched erect subshrub in T. johnwurdackiana ) and by its inflorescence, which is branched with the internode below dichasia 2.6–4.5 cm long (vs. inflorescence unbranched with flowers glomerulate at rachis nodes, with the internode below dichasia 0.4–1 cm long in T. johnwurdackiana ).

Full description: — Shrub ca. 1.5 m tall; branches terete, the uppermost vegetative internodes sparsely covered with proximally attached, rectangular to lanceolate scales 0.5–1.0 mm long with irregularly erose margins, the nodes with lanceolate scales 2–2.5 mm long. Leaves opposite and isomorphic. Petiole 9– 2 mm long covered with lanceolate scales 0.5– 1.0 mm long with irregularly erose margins. Lamina flat, lanceolate-ovate, 4–8 × 1.5–2.3 cm, chartaceous, base obtuse, apex acute, margin entire but covered with overlapping, clasping, folded scales, leaf surface on both sides strigose, covered with cylindric trichomes on the adaxial leaf surface and linear on the abaxial, both types adnate to surface for most of their length, the adnate portion covered with minute granulations (druses), trichome base forked or not and the free portion lanceolate with irregularly erose margins, trichomes on adaxial leaf surface 0.75–1.25 mm long, of this 30% free, trichomes on abaxial leaf surface 1.5–2 mm long, of this 10 to 20% free, and with a few short-stalked glands. Venation basally acrodromous with midrib plus two (to four) distal main veins with a smaller pair of main veins just inside the leaf margin, primary veins impressed adaxially with druses running along both sides of the veins, veins prominent abaxially and covered by rectangular to lanceolate scales 0.6–1.25 mm long, with irregularly erose margins. Inflorescence terminal, (reduced) thyrsoid, 3–22 cm long, internode below dichasia 2.6–4.5 cm, 5–18 flowers. Bracteoles two, 3.5–4 × 1.5 mm, short, right at base of bud, concave, lanceolate, apex acute, margin ciliate, outer surface covered with proximally attached lanceolate scales with irregularly erose margins, caducous later. Pedicels 2–3 mm. Flower perigynous, 5-merous; hypanthium (at anthesis) 9–9.5 × 5 mm, tubular to urceolate, strigose, covered with lanceolate scales 0.25–1 mm long with irregularly erose margins, scales larger among the calyx lobes, ca. 1.5 mm long; calyx tube ca. 0.6 mm long; calyx lobes 4.5–5.3 × 2–2.6 mm, persistent during fruit development, triangular, moderately covered with scales like those of the hypanthium except for a narrow marginal glabrous band, glabrous within, the margins ciliate. Petals purple, margin ciliate. Stamens 10, reddish, slightly dimorphic in size, geniculate, anther bent extrorsely (i.e., with dorsal side down), filaments with a few non–glandular long filamentous hairs, anthers subulate, apex attenuate, with an apical ventrally inclined pore, connectives with a cluster of long filamentous hairs on two ventral appendages ca. 0.6 mm long. Antepetalous stamens: filament ca. 10 mm long, pedoconnective ca. 1.6 mm long, thecae ca. 6 mm long. Antesepalous stamens: filaments ca. 11 mm long, pedoconnective ca. 4.5 mm long, thecae ca. 9 mm long. Ovary with base half adhered to hypanthium, with 5 locules, with congested setose hairs. Style 17–19 mm, filiform, glabrous, declinate; stigma truncate, papillose. Fruit a capsule, not seen mature.

Comments — Tibouchina rosanae is included in Tibouchina s. str. on the basis of the presence of scale-like trichomes covering the branches, petioles, nerves on the abaxial side of the leaf blade, and hypanthium. Tibouchina rosanae , as many species of Tibouchina s. str., may also be recognized by the connectives, which bear a cluster of long filamentous hairs on the two ventral appendages.

The main feature for the recognition of T. rosanae is the lax inflorescence. In this species the branches bearing terminal dichasia are long, with 2.6–4.5 cm. The internodes of the rachis are also long (4–7 cm). This architecture contrasts with that of the glomerular inflorescence with a crowding of dichasia, which is most common among Tibouchina with hairy connectives (section Barbigera ). Among these, longer branches are found in the Brazilian species T. araguaiensis Guimarães. (2014: 44) and T. edmundoi Brade (1959: 10) . These two species have the dichasium sustained by long branches, up to 4.5 cm long, and internodes of the rachis 5–8.5 cm long. Tibouchina bipenicillata ( Naudin 1850: 156) Cogniaux (1885: 385) , which occurs from Colombia and Venezuela to Costa Rica, also has relatively long internodes on the rachis (2.5–4 cm). Tibouchina rosanae can be separated from them by the life form and leaf trichomes ( Table 1).

Tibouchina johnwurdackiana Todzia has a very similar appearance to T. rosanae by the leaf indumentum, which has linear trichomes adnate to the surface for most of their length on both surfaces. However, T. johnwurdackiana is an unbranched erect subshrub, only to ca. 0.9 m tall, with glomerulate flowers on the nodes of the rachis ( Table 1).

Tibouchina rosanae is an amphistomatic species and the presence of stomata on the adaxial leaf surface is reported here for the first time in the genus.

Etymology: —This species is dedicated to Dr. Rosana Romero, in recognition of her contributions to the taxonomy of Neotropical Melastomataceae , particularly in tribe Microlicieae , and her skilled ability to supervise new students in the study of this botanical family.

Distribution and Habitat: — Tibouchina rosanae is recorded for ca. 290 m elevation, growing in patches of Amazon grassland vegetation on sandstone rocks (campos rupestres) in Xingu State Park, in the municipality of Santa Cruz do Xingu, Mato Grosso state, Brazil.

Conservation Status: —This species is known only by the type collection. Thus, the taxon is assessed as data deficient (DD).

Figures

FIGURE 1. Tibouchina rosanae P. J. F. Guim. & Woodgyer, sp. nov. A. Fertile habit. B. Node on stem with a larger scale. C. Lamina abaxial surface, base of blade and part of the petiole, venation basally acrodromous with midrib plus two (to four) distal main veins. D. Lamina abaxial surface, detail revealing linear trichomes. E. Lamina adaxial surface, base of blade and part of petiole, nerves impressed. F. Lamina adaxial surface, detail showing linear trichomes. G. Detached linear trichome from lamina adaxial surface. H. Bud with pedicel and bracteoles removed. I. Isolated lanceolate scale with portion of the hypanthium. J. Lateral view of antesepalous stamen. K. Style. L. Calyx lobes, hypanthium and pedicel with bracteoles after anthesis. Drawn from D.C. Zappi et al. 3217 (RB).

FIGURE 2. Tibouchina rosanae P. J. F. Guim. & Woodgyer, sp. nov. SEM images. A. Lateral branch of the inflorescence with rectangular to lanceolate scales. B. Middle portion of the hypanthium with lanceolate scales. C. Hypanthium at the insertion of the calyx lobes showing larger scales. D–F. Adaxial leaf surface. D. Linear trichomes. E. and F. Stomata. G–I. Abaxial leaf surface. G. Linear trichomes. H. Stomata and trichome. I. Glandular trichomes and stomata. SEM micrographs from D.C. Zappi et al. 3217 (RB).