Functional divergence exists in mucilage-mediated seed dispersal, but not in germination of myxospermic Lepidium campestre and Lepidium draba (Brassicaceae)

Abstract

The aim of this study was to compare the role of mucilage in seed dispersal and germination of the two closely related invasive weed species, Lepidium campestre and Lepidium draba. The study investigated the staining patterns of mucilage and its effects on seed germination, water uptake, dehydration, adherence to sand particles and dispersal by wind, water and animals following standard protocols. The mucilaginous seeds of L. campestre had a higher pectin and cellulose content than L. draba. This difference has a significant effect on water uptake and retention. The mucilage increased water uptake in both species, with L. campestre seeds absorbing significantly more water (836% compared to 75% in L. draba). Remarkably, the mucilage of both species had very little effect on seed germination. Significantly, the seeds of L. draba readily germinated under dry conditions, suggesting that this species may have developed different germination strategies. In addition, the seeds and fruits of L. draba showed a higher potential for dispersal via water and wind, whereas those of L. campestre adhered to animals. Further, L. campestre seeds showed significantly stronger adherence to sand particles (1872%) compared to those of L. draba (445%). This suggests that L. campestre seeds are more likely to disperse locally and possibly adhere to animals or soil particles. Our results suggest that mucilage produce by the two invasive weed species results in different methods of dispersal, which may help explain differences in their distribution patterns.