Pterolepis haplostemona Almeda & A.B. Martins, 2015

Almeda, Frank & Martins, Angela B., 2015, Pterolepis haplostemona (Melastomataceae): a new serpentine endemic from Goiás, Brazil, Phytotaxa 201 (3), pp. 233-238 : 234-237

Pterolepis haplostemona Almeda & A.B. Martins , sp. nov. ( Fig. 1 .)

Distinguished by its annual habit, simple unbranched hypanthial trichomes and intercalycine emergences, haplostemonous flowers, rostrate antesepalous stamens, short pedoconnective with conspicuous bilobed ventral staminal appendages, linear-lanceolate cauline leaf blades, calyx lobes tipped with a rigid simple erect trichome, and (3 −)4-locular ovary.

Type:― BRAZIL. Goiás: Município de Niquelândia ; 5 km após a Mina de Níquel da Companhia de Níquel Tocantins-CNT, 14˚22’18” S, 48˚23’13” W, 12 April 1996 (fl), R. C. Mendonça, R. Marquete, M. L. Fonseca & F. C. A. Oliveira 2446 (holotype: IBGE 38489 - image!; isotype: US!) .

Delicate wiry, annual herbs, 5−22 cm tall, branched or unbranched from the base, sparingly and openly branched distally. Cauline internodes quadrangular and obscurely winged at least distally, moderately to sparsely glandular hirtellous with widely to antrorsely spreading glandular trichomes 0.5 mm long. Nodal trichomes 1−2 mm long, simple and eglandular, erect or ascending. Basal leaves membranaceous, typically early deciduous and rarely present on flowering and fruiting plants; petioles 0.5 mm long, compressed and ill-defined, glabrous; blades 2−4 × 1−1.5 mm, elliptic, 1-nerved, bluntly acute to rounded apically, attenuate to obtuse basally, sparsely beset with smooth appressed or antrorsely spreading trichomes 0.5−1 mm long on both surfaces; margins entire. Cauline leaves membranaceous; petioles 1.2–2 mm long, sparingly beset with spreading simple or gland-tipped trichomes 0.5–1 mm long; blades 5–16 × 1–5 cm, narrowly elliptic to oblong-lanceolate, 1–3-nerved, acute apically and tipped with a simple trichome 0.5–1 mm long, acute to attenuate basally, sparsely beset adaxially with spreading gland-tipped trichomes mostly 0.5–1 mm long (free portion) that are adnate to the epidermis for ca 0.25 mm, also sparsely beset abaxially with gland-tipped trichomes 0.5–1 mm long that are not basally adnate to the epidermis; margins entire and sparingly beset with gland-tipped trichomes. Inflorescence a terminal laxly branched compound dichasium 3 × 10 cm long. Bracteoles on uppermost flowers 1–5 × 0.5–1 mm, narrowly elliptic; petioles 0.5–1 mm long, acute apically and basally, sparsely covered with spreading gland-tipped trichomes mostly 0.5 mm long, those on the adaxial surface are basally adnate to the epidermis, those on the abaxial surface are not, the margins entire and sparingly beset with glandular trichomes, the apical trichome 0.5–1 mm long. Hypanthium (fruiting) 3 × 2 mm, campanulate to suburceolate, moderately covered with spreading gland-tipped trichomes 0.5–1 mm long, the spreading trichomes on the toral region and intercalycine lobes externally 1–2 mm long, simple or gland-tipped. Calyx lobes (including 1–2.5 mm long apical gland-tipped or eglandular trichome) 3–4 mm long and 0.5–1 mm wide at the base, narrowly triangular, ± erect to antrorsely spreading at maturity, sparsely beset with trichomes like the hypanthium abaxially but glabrous adaxially. Petals 4, 5−5.5 × 3−3.5 mm, obovate with a minute basal claw, lilac or magenta, entire and eciliate with 1−3 apical or subapical gland-tipped trichomes 0.25−0.5 mm long. Stamens 4 (antesepalous); filaments 2.25−3 mm long; anthers 1.25−2 × 0.5 mm, yellow, subulate-rostrate, the apical pore ventrally inclined; connective somewhat thickened dorso-basally and prolonged 0.25 mm long or less below the thecae and expanded ventro-basally into an upturned or outwardly oriented bilobed appendage 0.5 mm long; staminodia absent. Ovary (at anthesis) superior, elliptic-ovoid. Style 4.5−5 mm long, ± straight; stigma punctiform. Pedicels (on fruiting hypanthia) 1.5−2 mm long, glabrous. Mature hypanthia 3 × 2−2.5 mm, campanulate to suburceolate, essentially equaling the enclosed capsule in length. Mature capsules loculicidal, ellipsoid to ± globose, 2 × 2 mm, (3−)4-locular, glabrous but crowned with a few (4−7) erect, simple trichomes mostly 0.25−0.5 mm long. Seeds 0.75 × 0.5 mm, cochleate, brown, the highest point toward the chalazal side. Raphal zone ovate to nearly circular, covering ca. 50% the length of the seed, testa regularly tuberculate.

Phenology:—Collected in flower and fruit in April, May, and June.

Habitat and distribution:—Presently known only from the Tocantins ultramafic complex (Macedo site), in Goiás, Brazil between 3 and about 18 km north of Niquelândia on both south and northwest facing ultramafic (serpentine) outcrops of rocky pyroxenite/peridotite and peridotite/dunite-based scree in the vicinity of nickel ore workings in campo limpo and campo sujo at 800–1000 m.

Conservation status:—The Macedo region north of Niquelândia in Goiás, Brazil is the center for Companhia Niquel de Tocantins (CNT), Brazil’s largest nickel mining and smelting operations ( Brooks et al. 1990). The known collections of Pterolepis haplostemona suggest that this rare and local species is restricted to a small area of the Macedo region. Because the CNT nickel mine has been developed as an opencast operation on one of the larger ultramafic massifs, it has substantially modified the original plant cover of this area. Based on georeferenced data from the known collections, GeoCAT ( Bachman et al. 2011) was used to calculate extent of occurrence (EOO) and area of occupancy (AOO) based on a user defined cell of 2 km. The extent of occurrence for P. haplostemona is 33.013 km ² and the area of occupancy is 20.000 km ². Using IUCN guidelines and criteria ( IUCN 2001, 2014) and its restricted extent of occurrence, annual habit with attendant fluctuations in the number of mature individuals each year, and ongoing mining threat that could drive the species to extinction in a short period of time, we assign this species a conservation status of Critically Endangered CR B1ab(iii).

Etymology:—The epithet for this species, haplostemona , refers to the reduced staminal series in which the number of stamens in each flower equals the number of petals and calyx lobes.

Additional specimens examined:— BRAZIL. Goiás: Macedo, ca. 15 km N of Niquelândia, 14˚18’ S, 48˚23’ W. South facing hill slope, stable peridotite/dunite-based scree and flat area below, ca. 500–800 m east of nickel workings. ca. 1000 m, on hillside, 21 April 1988 (fl & fr), R. R. Brooks, R. D. Reeves, A. J. M. Baker, & H. Dias Ferreira BRASPEX 163 ( NY!, UFG, US!) ; Macedo, ca. 15 km N of Niquelândia, 14˚18’ S, 48˚24’ W. NW facing hill slope and flat area adjacent to roadside below, about 1−1.5 km west of nickel ore workings. Ca. 1000 m, 22 April 1988 (fl & fr), R. R. Brooks, R.D. Reeves , A. J. M. Baker, & H. Dias Ferreira BRASPEX 177 ( NY!, UFG, US!) ; Niquelândia South Hill, southernmost ultramafic outcrop of the Tocantins Complex about 3 km from Niquelândia ,14˚27’ S, 48˚26’ W, 15 June 1990 (fl & fr), R. R. Brooks, R. D. Reeves, & H. Dias Ferreira TMEX 524 (K-image!, MO, UFG) ; Município de Niquelândia. Macedo , ca. 1 km da mina de níquel, 14˚21’29” S, 48˚23’11” W, 29 May 1996 (fr), M. Aparecida da Silva & G. Nunes de Jesus 2986 ( IBGE, US!) ; Niquelândia, Macedo , cerca de 18 km N de Niquelândia, 13 April 1992 (fl), T. S. Filgueiras & H. D. Ferreira 2276 ( IBGE 29859 -image!, US!) .

Discussion:—The diagnostic features of P. haplostemona are its narrow elliptic leaves, unbranched hypanthial and intercalycine trichomes,haplostemonous flowers with four antesepalous stamens, rostrate anthers, short pedoconnective, prominent ventro-basal anther appendages, and 3−4-locular ovary. Among neotropical genera of Melastomataceae assigned to the core Melastomeae , Pterolepis has traditionally been recognized by its conspicuously branched stellatepenicillate emergences on hypanthia and/or intercalycine sinuses. Pterolepis and Pterogastra ( Naudin 1850: 32) form a strongly supported clade based on molecular data but no morphological synapomorphies have yet been identified for this group ( Michelangeli et al. 2013). This new species has no branched emergences or trichomes on any of its vegetative or floral parts but it is otherwise a good match for Pterolepis in all other features including the adaxial foliar trichomes that are adnate to the epidermis basally for a portion of their length, prevailingly 4-merous flowers, a prominent setose trichome at the apex of each calyx lobe, and cochleate, tuberculate seeds. Some of its distinguishing features such as haplostemonous flowers and complete lack of branched emergences on hypanthia and calyx lobes suggest that it is a highly derived species that has evolved on ultramafic substrates. To our knowledge, no other species of Pterolepis is restricted to ultramafic substrates in Brazil or elsewhere in tropical America.

Students of the Melastomataceae had previously identified some of the first known collections of this species as Acisanthera (P. Browne 1756: 217) or Siphanthera (Pohl ex Candolle 1828: 121) . None of the species in either of these two genera have the distinctive adaxial foliar trichomes that are adnate to the epidermis basally for a portion of their length. Each of these two genera has seeds that differ from the seeds of Pterolepis . Acisanthera has seeds that are subcochleate to reniform with a foveolate testa and Siphanthera has seeds that are ellipsoid to lacrimiform or subreniform with an areolate testa. Except for the anomalous A. tetraptera ( Cogniaux 1885: 426) Gleason (1935: 206) whose affinities and exact generic placement remain unresolved, all species of Acisanthera and Siphanthera also differ from Pterolepis in having an ovary apex that is glabrous. There also appear to be modal differences in ovary locule number. Siphanthera has 2-locular ovaries and Acisanthera s.l. has 3-locular ovaries. In Pterolepis ovaries are modally 4-locular with some species that are 5-locular, and only a couple (including P. haplostemona ) that are (3−)4-locular.

In the most recent comprehensive account of Pterolepis ( Renner 1994) this new species keys closest to P. perpusilla ( Naudin 1844: 144) , Cogniaux (1885: 280) a widespread Brazilian annual (states of São Paulo, Minas Gerais, Goiás, Mato Grosso, and Distrito Federal) that has hypanthial trichomes that are unbranched but gland-tipped and intercalycine emergences that are branched, petals that are glandular-ciliolate, diplostemonous flowers with subisomorphic stamens, anthers with a truncate apical pore, and a consistently 4-locular ovary. Pterolepis haplostemona is also superficially similar to P. polygonoides ( Candolle 1828: 137) Triana (1871: 39) which can have (3−)4-merous flowers and many hypanthial emergences that are simple but with some in the intercalycine sinuses that are distinctly branched. This latter species, which grows on sandy soils in humid or swampy areas in cerrado and caatinga vegetation from Minas Gerais and Bahia north to Pernambuco, Piauí, Ceará and Maranhão, also differs in having glandular-ciliolate petals, diplostemonous flowers, subisomorphic stamens, and mostly solitary flowers in the upper leaf axils ( Renner 1994).

All collections of P. haplostemona have flowers that are haplostemonous. Evolutionary loss of fertile stamens is rare in neotropical species of the tribe Melastomeae . Among Melastomataceae generally, haplostemony is a characteristic feature of the Cyphostyleae , a tribe of three genera and 20 species that has capsular fruits derived from inferior ovaries ( Michelangeli et al. 2011), and the recently described monotypic genus Quipuanthus ( Michelangeli & Ulloa 2014: 533) that appears to have its closest affinities with the Cyphostyleae ( Michelangeli et al. 2014). Among neotropical genera with capsular fruits and superior ovaries, haplostemony is a consistent character state for five of the 15 species of Siphanthera , one species of Cambessedesia ( Candolle 1828: 110) , one species of Monochaetum (DC. 1828: 138) Naudin (1845: 48–49) , one species of Poteranthera ( Bongard 1838: 137) and various species in a few genera of the paleotropical Dissochaeteae and Sonerileae ( Bakhuizen 1943; Wickens 1975; Hansen 1982; Martins 1984; Hansen 1988; Cellinese & Renner 1997; Alvear 2010; Almeda & Robinson 2011; Kriebel 2012). Among berryfruited neotropical genera, only Blakea (P. Browne 1756: 323) appears to have a few haplostemonous species, all of which are restricted to southern Central America ( Almeda 2000; Penneys & Judd 2013).

Figures

FIGURE 1. Pterolepis haplostemona. A. Habit. B. Cauline leaf (abaxial surface). C. Flower in profile view. D. Petal (adaxial surface). E. Stamens (profile view on left and dorsal view on right). F. Capsule in cross-section showing three locules. G. Mature hypanthium and calyx lobes in profile view. H. Seed in profile view. (A–H from Mendonça et al.2446, US).