Volume 4 NOVONNumber 31994 Petroravenia (Brassicaceae), a New Genus from Argentina Ihsan A. Al-Shehbaz Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166-0299, U.S.A.ABSTRACT. Petroravenia eseptata Al-Shehbaz, anArgentinean new genus and species, is described andillustrated. Its relationships to Draba L., the NorthAmerican Cusickiella Rollins, and the South Amer-ican Eudema Humboldt & Bonpland, Onuris Phi-lippi, Sarcodraba Gilg & Muschler, and Dactylo-cardamum Al-Shehbaz are discussed. One of the Brassicaceae collections sent to MOby Stephan G. Beck (LPB) for determination wasan Argentinean plant that I put aside as a noveltyin Draba. Although the plant has almost fully de-veloped fruits, I did not dissect any of these toexamine the seeds. A loan of undetermined mustardsfrom Instituto de Botinica Darwinion (SI), Argen-tina, included another collection of the same speciesbut with dehisced fruits and mature seeds. It wasimmediately evident, for reasons given below, thatthe species cannot be accommodated in Draba orin any other known genus.KEY TO PETRORAVENIA AND SIMILAR GENERAla. Cotyledons accumbent; septum complete .. ....................... ........................ Drabalb. Cotyledons incumbent; septum absent or perforate, if complete then flowers solitary, filament bases pubescent, or seeds 1 or 2 per fruit. 2a. Flower 1 per branch; plants with numerous, fragile, fingerlike branches; fruit indehiscent, completely hidden between densely imbricate leaves; internodes rarely to 0.2 mm long; fruiting pedicels to 0.4 mm long .. ............................................ .............. Dactylocardamum 2b. Flowers few to numerous at the branch apex; plants unbranched or with stout, non-fingerlike branches; fruit dehiscent, readily visible; internodes more than 1 mm long; fruiting pedicels more than 1 mm long. 3a. Septum absent; sepals tomentose inside, ca. 2 x as long as petals; filaments flattened at least along the basal half; petals and filaments persistent even after fruit dehiscence ............ Petroravenia 3b. Septum perforate or complete; sepals glabrous inside, much shorter than petals; filaments terete; petals and filaments caducous soon after anthesis. 4a. Flowers solitary, borne on peduncles originating from the center of rosette; nectar glands 4 separate teeth, 1 on each side of the 2 lateral stamens ..........................-Eudema 4b. Flowers in (2-)6-25-flowered inflorescences; nectar glands in a ring. 5a. Seeds 1(-4) per fruit; plants of western United States ..................... Cusickiella 5b. Seeds 8-20 per fruit; plants of Argentina and southern Chile. 6a. Inflorescences bracteate; filaments glabrous at base; septum perforated ....... Onuris 6b. Inflorescences ebracteate; filaments pubescent at base; septum complete . . Sarcodraba The new genus, hereafter known as Petrorav-enia, is named in honor of Peter H. Raven, directorof the Missouri Botanical Garden, in recognition ofhis inspiration, encouragement, and continuous sup-port of the author's research.Petroravenia eseptata Al-Shehbaz, gen. et sp.nov. TYPE: Argentina. Prov. Salta/Jujuy: SanAntonio de los Cobres, 27 km hacia paso Huai-tiquina, Abra Chorrillos, conjines de Calamo-grostis sobre la arena, 4,560 m, 30 Dec. 1986,S. G. Beck 14136 (holotype, MO; isotype, LPB).Figures 1, 2. NovoN 4: 191-196. 1994.
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