Ravenelia cenostigmatis, a new rust fungus from Brazil

Abstract

Ravenelia cenostigmatis is described as a new species of plant rust (Uredinales) on Cenostigma gardnerianum (Caesalpiniaceae) from Brazilian Cerrado. Teliospore heads of R. cenostigmatis exhibit an unusually complex structure with four different kinds of cells: teliospore cells, sterile apical cells (intercalary between pedicel hyphae and teliospores), sterile hygroscopic cysts, and morphologically distinct border cells. The last are flattened, elaborately ornamented and probably sterile cells that are wedged between the teliospores and the cysts. Ravenelia cenostigmatis probably belongs to a natural assemblage of ravenelias that occur on caesalpiniaceous hosts and exhibit similar morphological traits. Key WordsCaesalpiniaceae; Kemkarnpella; systematics; teliospore morphology.The genus Ravenelia comprises about 190 species that are distributed in the subtropics and tropics around the world and infect almost exclusively members of Leguminosae. The telial morphology of Ravenelia species is unique: Complex teliospore heads are subtended by hygroscopic sterile cysts and consist of several teliospores and sterile apical cells (between teliospores and stalk hyphae). Similar teliospore heads occur only in the genus Spumula that cannot be sharply delimited from Ravenelia (Berndt, 1996) and in Kernkampella.A rust specimen recently collected on Cenostigrna gardnerianum Tul. (Caesalpiniaceae) in the Cerrado dry forest of NE Brazil was assigned to Ravenelia because of its typical teliospore heads and the leguminous host.The specimen was different from the only other Ravenelia on Cenostigma, R. spiralis Hennen & Cummins, and other members of the genus. It is therefore described as new. Ravenelia cenostigmatisFigs. 1-6 (etymology: named after the host genus, Cenostigma) Uredinia non observata. Urediniosporae solitariae, in teliis sparsae, ochraceae ad clare brunneae, late ellipsoideae, obovoideae vel subglobosae, 24-31 • 20-24/~m (Iongitudine media 27pm, latitudine media 22.2/~m), membrana indistincte bilaminata, ca. 2-2.5pm crassa, ad apicem leniter incrassata vel crassa usque ad 5-7(-9) /~m, lamina exteriore tenuissima, subhyalina, spiraliter denseque striata (spatium inter strias ca. 2/zm), striis delicate incisis, poris germinationis (2-)3(-4), prope hilum sitis. Telia abaxialia, dense sparsa, ca. 0.2-0.3 Part 179 of the series "Studies in Heterobasidiomycetous Fungi" of the Botanical Institute, University of T6bingen ~ Corresponding author. E-mail: reinhard.berndt(~uni-tuebingen.de mm diametro, atrobrunnea, complanate globuliformes, paraphysibus periphericis copiosis, incurvatis, ca. 55-130• pariete aurantiaco, dorsaliter et ad apicem valde incrassato. Capitulae teliosporarum castaneae, globosae, subglobosae vel late ellipsoideae, 60-100 [tm diametro, ex 3-6 cellulis in omni directione compositae, teliosporae unicellulatae, sporae centrales 18-27x 15-20/~m (Iongitudine media 21.3/~m, latitudine media 18/~m), membrana bilaminata, exteriore tenui, subhyalina, verrucis inconspicuis, latis et applanatis dense sitis, interi...