Aspilia africana is a common tropical weed whose seeds are readily dispersed by human activity. The seeds have small hooks and barbs on their surface that cling to clothing, shoes, farm tools, and equipment. As farmers move between fields or transport harvested crops, these seeds are inadvertently carried along and deposited in new locations. This makes human-aided dispersal the primary mechanism by which Aspilia africana spreads.
Emilia sonchifolia (tassel flower) produces light, feathery seeds with a pappus that are primarily dispersed by wind, not by human contact. Boerhaavia diffusa (spreading hogweed) can spread through sticky fruits, but wind and water are its main dispersal agents. Bougainvillea species are ornamental plants propagated deliberately by humans through cuttings, but they are not classified as weeds in the agricultural sense.
Exam tip: When a question asks about dispersal "by man," it typically refers to unintentional transport of weed seeds on clothing, tools, or farm produce - not deliberate planting.
