The avoidance of interference between the presentation of pollen and stigmas in angiosperms II. Herkogamy

Abstract

Herkogamy is the spatial separation of pollen presentation and pollen receipt within or between blossoms of an individual plant. Several classes of herkogamy are recognised; these are defined by whether all blossoms are identical (homomorphic herkogamy), all blossoms dispatch and receive pollen but reciprocal forms occur (reciprocal herkogamy), or some or all blossoms perform only one function (interfloral herkogamy). Within homomorphic herkogamy, unordered herkogamy, in which pollinator contacts with stigmas and pollen within a blossom are many and occur in no particular sequence, is distinguished from ordered herkogamy in which contacts are few and ordered. For ordered herkogamy further divisions are based on the operation of the pollination mechanism.Herkogamy is usually interpreted as a mechanism which reduces self-fertilisation and promotes outcrossing. However, as many herkogamous plants are also self-incompatible, it is suggested that the various classes of herkogamy also function in part or solely as mechanisms which avoid interference between pollen receipt by stigmas and pollen dispatch from anthers. Although for herkogamous blossoms these two functions are separated in space, many such flowers control pollinator behaviour so that both pollination surfaces are contacted during a single visit. In dichogamous blossoms separation of pollen dispatch and receipt is temporal rather than spatial and this difference has several important consequences for the pollination biology of dichogamous and herkogamous blossoms.

Mixed Mating in Homostylous Species: Genetic and Experimental Evidence from an Alpine Plant with Variable Herkogamy,Primula halleri

“…Herkogamy is widely interpreted as a key floral trait that reduces interactions between male and female floral functions (Barrett 2002) and, importantly, prevents autogamy in selfcompatible plants (Webb and Lloyd 1986). Its occurrence in self-compatible, monomorphic (i.e., homostylous) primrose species that evolved from obligately outcrossing, heterostylous ancestors (Mast et al 2006;de Vos et al 2014ade Vos et al , 2014b) is therefore enigmatic.…”

“…In this study, we investigate the reproductive consequences of variation in one important floral trait: the spatial separation between male and female reproductive organs (i.e., herkogamy; Webb and Lloyd 1986). Although the preponderance of studies indicates that greater separation between sexual organs favors outcrossing, the effects of herkogamy on plant reproduction may be complex and remain poorly documented, especially when herkogamy decreases through anthesis.…”

Outcrossing rates of individual Mimulus ringens genets are correlated with anther–stigma separation

“…Increased anther-stigma separation may reduce the amount of self-pollen deposited on the stigma, potentially increasing the proportion of ovules fertilized by outcross pollen (Ennos, 1981;Webb & Lloyd, 1986;Lloyd & Schoen, 1992).…”

Biologia floral e visitantes de Gaylussacia brasiliensis (Spr.) Meissner (Ericaceae) - uma espécie com anteras poricidas polinizada por beija-flores

“…No entanto, G. brasiliensis apresenta hercogamia que impede que o pólen da mesma fl or entre em contato com o estigma. A hercogamia de aproximação apresentada por G. brasiliensis parece ser comumente encontrada em outras plantas, tendo as estruturas reprodutivas localizadas de forma que o estigma seja contactado em primeiro lugar pelos polinizadores (Webb & Lloyd 1986;Freitas et al 2006). Embora a separação espacial das anteras e estigmas dentro de uma mesma fl or seja considerada uma adaptação que limita a autopolinização, a hercogamia como promotora da polinização cruzada nem sempre funciona (Medrano et al 2005).…”