Two new species of Croton L. (Euphorbiaceae) from campos rupestres of Minas Gerais State, Brazil1

Journal of the Torrey Botanical Society, Apr-Jun 2009 by Medeiros, Debora, Valle, Luci de Senna, Alves, Ruy Jos� Valka

MEDEIROS, D., L. SENNA-VALLE, AND R. J. V. ALVES (Department of Botany, Museu Nacional, Universidade Federal do Rio de Janeiro, 20.940-040, Rio de Janeiro, RJ, Brazil). J. Torrey Bot. Soc. 136: 186-191. 2009.-Two new species of Croton L. (Euphorbiaceae) from campos rupestres of Minas Gerais State, Brazil. Two new species of Croton L. (Euphorbiaceae) are described and illustrated. Croton lenheirensis and C. pradensis occur in campo rupestre vegetation on quartzitic soils in the State of Minas Gerais, the former from Serra do Lenheiro in S�o Jo�o del Rei and the later from Serra de S�o Jos� in Tiradentes. Both localities are within an important center of endemism for Croton sect. Medea (Klotzsch) Baill., which is represented by at least 30 species from South America. Taxonomic characters which circumscribe the Section are subshrub and shrub habit, laciniate or glandular stipules, stellate indumentum, distribution of glands at the margins of either laciniate or entire sepals of the pistillate flowers, and multifid styles. Croton lenheirensis morphologically resembles C. gnidiaceus Baill., but differs by triangular stipules, lack of petals in pistillate flowers and of apressed-stellate trichomes. Croton pradensis shares morphological characters with C. vestitus Spreng. and C. josephinus M�ll. Arg., species also represented on Serra de S�o Jos� flora, but it is easily distinguishable from both by its wooly sparse indumentum and pistillate flowers which present entire eglandular sepals and no petals.

Key words: Brazil, campo rupestre, Croton sect. Medea, Euphorbiaceae, Minas Gerais.

Webster (1993) recognized 40 sections within the genus according to morphological characters used by Baillon (1864) and M�ller Argoviensis (1873) and to geographical distribution data. Croton sect. Medea (Klotzsch) Baill. is represented by at least 30 species from South America. Relevant taxonomic characters within the Section are subshrub and shrub habit, laciniate or glandular stipules, stellate indumentum, contracted inflorescences, distribution of glands at the margins of either laciniate or entire sepals in pistillate flowers, and multifid styles.

With regard to phytogeographic data, most of Medea species are restricted to campo rupestre areas that are widely known for high endemism and biodiversity. The Serra do Lenheiro and Serra de S�o Jos� belong to the Tiradentes geological Formation, a marine quartzite succession of Precambrian age (Ebert, 1957). This area is an important center of endemism for Croton sect. Medea (Klotzsch) Baill., since these ridges together present six species of C. sect. Medea (five of them endemic, so far), a reasonable number when it is compared to the taxonomical diversity within this genus registered in other campo rupestre sites in Minas Gerais State. Furthermore, the Serra de S�o Jos� is Environmental Protection Area.

Material and Methods. Field work was conducted in 2000-2006, with an intense search for Croton sect. Medea in at least 30 campo rupestre localities in the State of Minas Gerais. Populations were randomly sampled at each locality and some individuals were monitored throughout the year. Morphological data were obtained from a total of 22 individuals of C. lenheirensis in the Serra do Lenheiro and 15 of C. pradensis in the Serra de S�o Jos�. Plant material is deposited in the Herbario do Museu Nacional (R), Herbarium Bradea (HB) and Jardim Bot�nico do Rio de Janeiro (RB). This research was developed as part of the doctoral project of the first author at the Programa de Pos-Graduac�o em Ciencias Biol�gicas (Bot�nica), Universidade Federal do Rio de Janeiro.

Results. Dichotomous key to the species of Croton sect. Medea (Klotzsch) Baill, from campos rupestres in Serra do Lenheiro and Serra de S�o Jos� areas (a summary of taxonomic characters for these species is given in Table 1).

1. Subshrubs, inflorescences reduced, indumentum absent .... Croton arlineae 1'. Subshrubs, inflorescences reduced, indumentum stellate .............. 2

2. Petals of the pistillate flower subflabeliform; indumentum lanose inconspicuous, leaves apparently glabrous .................. C. gnidiaceus

2' . Petals of the pistillate flower absent or reduced; indumentum lanose, conspicuous, dense .................. 3

3. Sepals of the pistillate flower eglandular; indumentum lanose concentrated at the margin and main vein of the leaf .................. C pradensis

3'. Sepals of the pistillate flower glandular; indumentum uniformely distributed at the leaf .................. 4

4. Stipules entire, triangular, glandular; sepals of the pistillate flower entire and petals absent ....... C lenheirensis

4'. Stipules lanceolate, laciniate, glandular; sepals of the pistillate flower laciniate, petals reduced, glanduliform . 5

5. Margin of the leaf entire; stipules 2-3 mm long; petal of the staminate flower glabrous at both faces, filaments and anthers completely pilose .................. C. josephinus

5'. Margin of the leaf laciniate, glandular; stipules 4-7 mm long; petal of the staminate flower pilose at adaxial face and glabrous at abaxial face, filaments pilose at the base and anthers glabrous ................ C. vestitus