Intraspecific neighbour effects on the growth and morphological plasticity of Salvinia molesta

Abstract

The tropical fresh water fern salvinia(Sa1vinia mlesta D.S. Mitchell) ' is a problematic weed and is being controlled biologically by the introduction of a weevil, Cyrtobagous salviniae. The plant consists of three morphologically different growth forms; primary, secondary and tertiary, duringitsgrowth. The present paper describes how the initial density of primary stage plants affected its morphological plasticity. Primary stage apical cuttings consisting of three ramets (uniform in size) were selected and were grown at densities of 16,400 and 800 ramets per square metre. The growth and morphological changes were observed for a period of 100 d. Plants remained at their primary stage under the lowest density and they transformed from primary to secondary and then to tertiary growth stages at higher densities. There were significant differences between the growth forms and their growth.

Endocide-Induced Abnormal Growth Forms of Invasive Giant Salvinia (Salvinia molesta)

“…The experiment showed that increasing density generally reduced branching of S. molesta . This result is consistent with the previous observations 12 , 13 , 16 , 19 .…”

“…It has been commonly recognized that the following relationship is present between the growth forms (stages) and density 16 , 21 , 29 : primary growth stage (form A or B) occurs in adverse conditions or during the initial invading stage of the infestation and thus the population density is low; the secondary stage is found in open water (either freely or on the edge of stable mats); and the tertiary stage (form L) occurs only under higher density. It seems that population density or crowding condition is the primary cause of the growth stages (forms) in S. molesta .…”

“…It generally accepted that S. molesta exhibits three distinct growth forms: “primary-invading form”, “open-water-colonizing-form”, and “mat-form” 13 . The primary-invading form exhibits small, delicate leaves (i.e., <15 mm wide), whereas the leaves of the secondary-colonizing form are slightly cupped and larger (i.e., 20 to 50 mm wide), and in the tertiary-mat form the leaves have reached maximum size (i.e., up to 60 mm wide), are deeply keeled, and have sporocarps 13 , 15 , 16 , 19 – 21 , 29 . These three growth forms may appear sequentially during invasion such that some investigators have proposed that there is continuity of growth between them 36 .…”

“…These three growth forms may appear sequentially during invasion such that some investigators have proposed that there is continuity of growth between them 36 . Some researchers have used phenotypes, forms, stages, or phases to refer these forms, even in the same publications, because these forms acted as the developmental phases 14 – 16 , 21 . However, others have described these forms more generally as growth stages 19 , 25 , 29 .…”

The effects of ramet density on growth and branching of Salvinia Molesta

“…15 The effect of density of plants on its morphological plasticity has also been studied. 16 In thick growing mats of S. molesta (i.e. at the tertiary stage) density stress is unavoidable.…”