Biological flora of the British Isles: Cakile maritima Scop

Abstract

1 This account reviews information on all aspects of the biology of Cakile maritime that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles : distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. 2 Cakile maritime (sea rocket) is a succulent, annual species that is confined to maritime strandlines on sand or shingle, and associated foredunes. British material is ssp. Integrifolia (= ssp. Maritime ), found around the Atlantic and Mediterranean coasts of Europe. Cakile maritime shows considerable variation, within and between subspecies, especially in fruit morphology and leaf shape. A very closely related species, Cakile edentula , is native to the east coast of North America. Both species have been introduced to Pacific North America and Australia. 3 Populations of C. maritime tend be ephemeral and shifting, depending on dispersal by tides and wind. The fruits are 2-segmented: the distal segments are readily detached and can float considerable distances in seawater; the proximal segments tend to shed their seed while attached to the maternal plant. Seeds require cold stratification and do not germinate at high salinity, or usually while retained in intact fruit segments. There is often a flush of germination in strandlines left by early season, equinoctial spring tides. Cakile maritime shows great phenotypic plasticity of form and reproductive output. Work on C. edentula suggests that abundance is regulated by a combination of density-dependent and density-independent processes. Landward dispersal of seeds from strandline populations may subsidise foredune populations, which themselves experience severe mortality from predators. 4 Cakile maritime is tolerant of salt spray and transient seawater inundation. Al though beach and dune sand is a meagre source of macronutrients, C. maritime shows large growth responses to nitrogen addition and can exploit local nitrogen enrichment associated with mineralisation of organic detritus washed up on the strandline. Growth is stimulated by burial with blown sand and plants sometimes form the nuclei of early successional foredunes. The tissues are rich in glucosinolates; these may be responsible for the limited ranges of herbivores and fungal pathogens, and the absence of mycorrhiza.