Phylogenetics in Clarkia (Onagraceae): Restriction Site Mapping of Chloroplast DNA

Restriction site maps of chloroplast DNA (cpDNA), maternally inherited in Clarkia, were obtained in representative species of all seven diploid sections, the allotetraploid sect. Clarkia, and the outgroup Epilobium brachycarpum. CpDNA restriction site variation was analyzed by Wagner and Dollo parsimony, bootstrapping, and genetic distance methods. Four shortest Wagner trees, one of which was also the shortest Dollo and Bootstrap majority-rule tree, were examined along with 21 one-step longer trees. Section Myxocarpa was placed as basal in Clarkia followed by a trichotomy of the Rhodanthos lineage, the Eucharidium I Clarkia lineage, and the lineage including sects. Sympherica, Phaeostoma, Fibula, and Godetia. However, when trees only one step longer are considered, many of these sectional alignments are lost. Early and rapid divergence of most sectional lineages, coupled with higher rates of cpDNA restriction site homoplasy, is proposed to account for the lack of many synapomorphic restriction site characters at the sectional level in Clarkia. A comparison of the cpDNA results to morphology, cytology, and biogeography with respect to intersectional relationships is presented. Diploid sect. Fibula, previously believed to have originated through intersectional crossing between sects. Phaeostoma nd Sympherica, has a chloroplast genome similar to one species of sect. Phaeostoma. Monophyletic lineages as previously described on the basis of the distribution of duplicated PGI genes are supported, but not fully so. The origin of the allotetraploid C. pulchella involved sect. Eucharidium as the maternal diploid parent and sect. Myxocarpa as the paternal diploid parent. The origin of C. pulchella was ancient, predating the divergence of the two extant species of sect. Eucharidium. Clarkia is a distinctive genus in the tribe Onagreae (Onagraceae) and comprises approximately 44 annual species with all but one, the polyploid C. tenella complex in South America, endemic to western temperate North America. The landmark monograph of Clarkia by Lewis and Lewis (1955) pulled together Clarkia, Eucharidium, Godetia, and Phaeostoma on the bases of floral and vegetative morphology, chromosome number, and crossing relationships. Ten sections were recognized with diploid species confined to seven: Sympherica (formerly Peripetasma), Fibula, Phaeostoma, Eucharidium, Godetia, Rhodanthos (formerly Primigenia), and Myxocarpa. Polyploid species derived from intersectional crosses were placed in sects. Clarkia, Biortis, and Connubium, while the polyploid species from intrasectional crosses were placed in the parental diploid section. Subsequent researchers have stressed the naturalness of Clarkia based on morphological and cytological evidence (Raven 1979, 1988) and on genetic evidence (Gottlieb and Weeden 1979; Pichersky and Gottlieb 1983). Putative relationships among the seven sections containing diploid species and polyploid sect. Clarkia are depicted in figure la. Ancestral clarkias are considered to have relatively large, lavender-pink, bowl-shaped (godetia-type) flowers with petal markings. These clarkias are self-compatible but outcrossed, possess the chromosome gametic number n = 7, and have a relatively northern distribution (Lewis 1980). Such ancestral clarkias now best fit in the extant sect. Rhodanthos. Speciation in Clarkia has, thus, occurred primarily within habitats distributed from north to south and from mesic to xeric. Evolution has resulted in new morphological traits such as floral tubes (sects. Eucharidium and Clarkia), reduction in stamen number (sect. Eucharidium), changes in inflorescence architecture (several sections), extensive repatterning of the chromosomes with subsequent increasing and decreasing aneuploidy and polyploidy