Clonality in the Endangered <Emphasis Type="Italic">Ambrosia pumila</Emphasis> (Asteraceae) Inferred from RAPD Markers; Implications for Conservation and Management

Clonal plants have the ability to spread and survive over long periods of time by vegetative growth. For endangered species, the occurrence of clonality can have significant impacts on levels of genetic diversity, population structure, recruitment, and the implementation of appropriate conservation strategies. Here we␣examine clone structure in three populations of Ambrosia pumila (Nutt.) Gray (Asteraceae), a federally endangered clonal species from southern California. Ambrosia pumila is a perennial herbaceous species spreading from a rhizome, and is frequently found in dense patches of several hundred stems in a few square meters. The primary habitat for this species is upper terraces of rivers and drainages in areas that have been heavily impacted by anthropogenic disturbances and changing flood regimes. RAPD markers were employed to document the number and distribution of clones within multiple 0.25 m² plots from each of three populations. Thirty-one multi-locus genotypes were identified from the 201 stems sampled. The spatial distribution of clones was limited with no genotypes shared between plots or populations. Mean clone size was estimated at 9.10 ramets per genet. Genets in most plots were intermingled, conforming to a guerrilla growth form. The maximum genet spread was 0.59 m suggesting that genets can be larger than the sampled 0.25 m² plots. Spatial autocorrelation analysis found a lack of spatial genetic structure at short distances and significant structure at large distances within populations. Due to the occurrence of multiple genets within each population, the limited spread of genets, and a localized genetic structure, conservation activities should focus on the maintenance of multiple populations throughout the species range.