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.
Highlights
Importance value index (IVI) was highest in case of A. adenophora (198.38) among all members in the studied quadrats made a strong point to conclude the species as a notorious which dominate over the community and outnumbers the other members present in the colony where it belongs
Invasive species are described by several aspects as they have been introduced by human activity into ecosystems where they are not native, and they have established populations of advantageous fast growing and self-reproducing, causing significant changes in pre-existing ecosystems (Richardson, 1994)
Ageratina adenophora, a non-mangrove member from the Asteraceae family, shows a nice pattern of induced pseudo-viviparous germination, as a result of the high monsoon rainfall. By this mode of reproductive strategy clumps of germinating propagules develop on the fully matured heads still attached with the mother plants
Summary
Ageratina adenophora (Spreng.) R.M. King & H. The plant is commonly known as crofton weed or sticky eupatorium, being other local common names as sticky snakeroot, Mexican devil, and cypress weed in USA, New Zealand and India, respectively. It is native to central Mexico and thereby introduced in many other countries as an ornamental plant. This new comer has established and spread over the regions and became an invasive species. Ageratina adenophora was introduced in India after 1498 (Biswas, 1934). At present, it is an important alien species in Indian flora. The plant rated as class-iv noxious weed under NSW (New South Wales) noxious weed act, 1993
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