Dimorphic Incompatibility in Turnera Hermannioides Camb. (Turneraceae)

Abstract

Turnera hermannioides (Turneraceae) is a distylous, diploid, perennial restricted to open, sandy sites in northeastern Brazil. Four populations sampled in Sergip6 contained equal proportions of longand short-styled plants. The style and stamen dimorphism in floral morphs is associated with differences in pollen size and pollen production. In contrast, flower size, ovule number, and seed fertility of the morphs are not significantly different. A controlled pollination program demonstrated that individuals of T. hermannioides possess a selfand intra-morph incompatibility system. The only pollinations resulting in significant seed production were between the floral morphs. Populations of T. hermannioides grow intermingled with T. ulmifolia, a widespread polymorphic complex containing forms that resemble T. hermannioides. A crossing program between T. hermannioides and diploid and tetraploid varieties of T. ulmifolia revealed barriers to hybridization particularly in crosses at the diploid level. It is concluded that T. hermannioides is a restricted diploid species that is reproductively isolated from T. ulmifolia. Distyly is reliably reported from 23 flowering plant families (Ganders, 1979). In taxa on which experimental work has been undertaken, it has usually been shown that the stamen-style dimorphism is closely associated with a diallelic self-incompatibility system as well as several morphological polymorphisms involving pollen size, pollen production, and stigmatic papillae number and length. Although there is general agreement that distyly is an outbreeding mechanism (Darwin, 1877; Crowe, 1964; Vuilleumier, 1967), the functions of the various floral polymorphisms that accompany self-incompatibility are still unclear (Yeo, 1975; Ganders, 1979). The large neotropical genus Turnera (Turneraceae) contains some 54 species of which 37 are reported to be heterostylous (Urban, 1883). Species within the genus are poorly defined, and there is need for a modem taxonomic revision of the group. With the exception of studies of distyly in the widespread polymorphic weed complex T. ulmifolia L. (including the synonyms T. subulata Smith and T. trioniflora Sims) by Lock (1904), Barrett (1978), and Bentley (1979), there are no published reports of experimental work on the reproductive biology of species of Turnera. To broaden understanding of the nature of distyly in the genus, we initiated a study of the breeding system of T. hermannioides, a herbaceous to woody perennial native to northeastern Brazil. In addition to documenting general features of distyly, incompatibility relationships, and population structure in the species, we also investigated its crossing relationships with T. ulmifolia, with which it is superficially similar in habit (Urban, 1883) and frequently sympatric. MATERIALS AND METHODS All populations of Turnera hermannioides studied occur in the state of Sergipe in northeastern Brazil. Detailed localities are presented in Table 1. At each population, the number of longand short-styled plants was recorded. In populations 2, 3, and 4, the entire flowering population was scored whereas in population 1, a complete sample of the accessible part of the population (ca. one-third of the total size) was made (Table 5). Deviations from the expected 1: 1 morph frequency were analyzed using the G-statistic which was calculated for each population. In addition, pooled and heterogeneity G-statistics were calculated (Sokal & Rohlf, 1981) to examine whether population structures were similar. I We thank the staff of the herbarium at the Instituto Pesquisas Agronomicas, Recife, Pernambuco for assistance, NSERC Canada for funding field studies in northeastern Brazil, and Maria Mercedes Arbo for aid in securing seed collections of Turnera ulmifolia. This paper is dedicated to the memory of the late Professor Ddrdano de Andrade-Lima, authority on the flora and vegetation of northeastern Brazil, who introduced one of us to Turnera. 2 Department of Botany, University of Toronto, Toronto, Ontario M5S 1Al, Canada. ANN. MISSOURI BOT. GARD. 72: 259-263. 1985. This content downloaded from 157.55.39.144 on Mon, 25 Jul 2016 04:53:55 UTC All use subject to http://about.jstor.org/terms 260 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 72 TABLE 1. Localities of Turnera hermannioides and Turnera ulmifolia populations used in this study. All populations of T. hermannioides were collected along roadsides on open, waste ground. A. Turnera hermannioides Varieties of T. ulmifolia Population Locality Present at Site la Hwy. 235, ca. 30 km W of Itabaiana, Sergip6 elegans 2 Hwy. 235, ca. 15 km W of Itabaiana, Sergipe elegans 3 Hwy. 235, ca. 1 km W of Itabaiana, Sergip6 elegans 4b Hwy. 235, 21 km S of BRI01, near Aracaju, Sergip6 elegans and surinamensis B. Turnera ulmifolia