A survey of reproductive biology in Onagraceae

Abstract

Onagraceae constitute a clearly marked family of the order Myrtales, comprising 7 tribes, 17 genera, and about 674 species. Of these species, about 42% are outcrossed, 52% self‐pollinated, and another 6% contain both sorts of breeding systems within a single species. In outcrossed species, the stigma is always elevated above the anthers at anthesis. The three principal modes of enforcing outcrossing are protandry, in Epilobium , Clarkia , and Lopezia (with protogyny in most species of Circaea ); male sterility, independently derived in four small sections of Fuchsia ; and genetic self‐incompatibility, found in at least 76 species, representing 4 of the 7 tribes and 10 of the 17 genera of the family. Nearly all of the trees and shrubs in the family, but only about one third of the annuals and perennial herbs, are outcrossing. Clarkia is an example of an entirely annual genus that consists predominantly of outcrossing species, whereas Ludwigia and Epilobium are predominantly perennial genera that consist of a majority of self‐pollinating species (and, in contrast to Clarkia, are largely polyploid). Less than one fifth of the trees, shrubs, and annuals in Onagraceae, but about 60% of the perennials, are polyploid. Aneuploid changes in chromosome number and the evolution of complex heterozygotes, the latter represented by 52 species of 4 different genera of the tribe Onagreae, take place largely among annual species in this family. Data summarised for the pollination systems of the approximately 283 modally outcrossing species of Onagraceae indicate that 37% of the species, representing 12 genera, are bee‐pollinated; 31% bird‐pollinated; 17% hawkmoth‐pollinated; 7% pollinated by syrphid and tachinid flies; 6% noctuid‐pollinated; and 0.4% (1 species: Clarkia concinna ) by a combination of cyrtid flies and butterflies. No species is known to be modally pollinated by bats, by beetles, or by wind, and none has apomixis involving seeds, nor heterostyly. Some 22 individual shifts in pollination system would be sufficient to account for the evolution of the roughly 283 outcrossing species of the family, but an additional number of shifts probably involving at least 300 events would be necessary to account for the evolution of the 353 modally autogamous species. The repeated evolution of autogamy is clearly the most important evolutionary process involved in the multiplication of species of Onagraceae.