First evidences for induced pseudo-viviparous germination in Ageratina adenophora (Crofton weed), a common alien weed of Darjeeling Himalaya, India

Abstract

In the present investigation, an autecological study has been carried out for Ageratina adenophora (Spreng.) R.M. King & H. Rob., a common aggressive alien weed found in dense patches at different localities of Darjeeling Himalaya, West Bengal, India. Single generation colony, derived via induced pseudo-viviparous germination, outnumbers the associated species by its aggressiveness and allelopathic potentiality. The cypselae (fruits) mature during full monsoon and being laden with water droplets shed their deciduous calyx (pappus). The later thus cannot disperse away from the head (capitulum) by effective parachute mechanism. Very frequently, many of the cypselae get germinated with two minute paracotyledons on the receptacle that still attached with the mother plant by decaying receptacle stalk. Entire head with cluster of seedlings, becoming heavy by monsoon shower, drops down on the lower wet substratum. It is the beginning of the colony formation. Vigorous growth and allelopathic potentiality of the species decreases the establishment, growth and density of other plant species in that area facilitating procurement of more space and nutrients for the individuals by itself, leading to make a dense colony with very high Importance Value Index (IVI). All these features may be considered as an adaptation to maintain its invasiveness and dominance over the surrounding species.