Four New Distylous Species of Waltheria (Sterculiaceae) and a Key to the Mexican and Central American Species and Species Groups

Abstract

Four new distylous species of Waltheria endemic to Mexico are described and illus- trated: W. bicolor from Colima, W. fryxellii from Mexico, Guerrero, Michoacan, and Jalisco, W. lundelliana from Nayarit, and W. tridentata from Guerrero, Puebla, and Oaxaca. Stigmatic and pollen dimorphisms between pin and thrum flowers are described for the new species and placed within the context of those dimorphisms found in other Mexican and Central American Waltheria species. Three species groups, based partially on stigma types (pin-clavate, fan-plumose, and elon- gate-plumose), are newly described and all Mexican and Central American species delineated to them. All four new species belong to the newly designated crest-flowered waltherias, characterized by possession of crest-like inflorescences, clavate pin stigmas, ovoid chartaceous capsules with partially loculicidal dehiscence, and bracteal trichomes that are exclusively stellate. A key to the 15 Mexican and Central American species is provided and their geographical distributions are illus- trated. Waltheria is a primarily neotropical genus of approximately 50 species. Although one species is herbaceous, most are shrubs or subshrubs that flower for several months, producing a few open flowers at each node that remain open up to one day. In Mexico, species usually occur in semiarid areas in the Caribbean Floristic Region (Rzedowski 1978). The two centers of diversity for the genus are Mexico, with 15 species (Fig. 1), and Brazil, with approximately 25 species. The genus consists of many species with local- ized or regional distribution, with approxi- mately 20 species endemic to Brazil, and nine species endemic to Mexico (Table 1): W. aca- pulcensis, W. acuminata, W. bicolor, W. conzattii, W. fryxellii, W. lundelliana, W. preslii, W. pringlei, and W. tridentata. Waltheria detonsa A. Gray is an en- demic to the biogeographic province connect- ing northern Mexico and southeastern Arizona. Except for the pantropical W. indica, the distri- butions of the remaining species found in Mex- ico extend into Central or South America (Table