Petroravenia eseptata Al-Shehbaz, an Argentinean new genus and species, is described and illustrated. Its relationships to Draba L., the North American Cusickiella Rollins, and the South American Eudema Humboldt & Bonpland, Onuris Philippi, Sarcodraba Gilg & Muschler, and Dactylocardamum Al-Shehbaz are discussed. One of the Brassicaceae collections sent to MO by Stephan G. Beck (LPB) for determination was an Argentinean plant that I put aside as a novelty in Draba. Although the plant has almost fully developed fruits, I did not dissect any of these to examine the seeds. A loan of undetermined mustards from Instituto de Botanica Darwinion (SI), Argenina, included another collection of the same species but with dehisced fruits and mature seeds. It was immediately evident, for reasons given below, that the species cannot be accommodated in Draba or in any other known genus. KEY TO PETRORAVENIA AND SIMILAR GENERA la. Cotyledons accumbent; septum complete Draba Ib. 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 Petroravenia, is named in honor of Peter H. Raven, director of the Missouri Botanical Garden, in recognition of his inspiration, encouragement, and continuous support of the author's research. Petroravenia eseptata Al-Shehbaz, gen. et sp. nov. TYPE: Argentina. Prov. Salta/Jujuy: San Antonio de los Cobres, 27 km hacia paso Huaitiquina, Abra Chorrillos, conjines de Calamogrostis 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. This content downloaded from 157.55.39.45 on Fri, 02 Sep 2016 06:03:15 UTC All use subject to http://about.jstor.org/terms
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