Gaertn.
Description
Sphaeranthus indicus Gaertn. is a widespread weedy annual of the Old World tropics and subtropics, with a very broad GBIF footprint (over 1200 occurrences) spanning India, Sri Lanka, Bangladesh, Nepal, Bhutan, Myanmar, Thailand, Laos, Vietnam, southern China and Indonesia, and extending to Australia, Madagascar, Kenya and Ethiopia. It is a plant of seasonally wet, open ground: rice-field margins, fallows, ditches, damp wastelands and the receding edges of pools and tanks, mostly at low elevations. The specimen photographed at Mewa-Khola in Nepal at 1100 m in April occurs in the warm subtropical foothill belt at the upper margin of its lowland range, where post-monsoon wet ground provides its preferred germination sites.
It is a strongly aromatic annual herb with a much-branched, often reddish, ascending to spreading stem bearing conspicuous toothed or undulate wings formed by the decurrent leaf bases. The leaves are obovate to oblanceolate, sessile, and serrate-dentate. The diagnostic feature is its compound capitulescence: numerous tiny, narrow secondary heads are aggregated into a dense, globose to ovoid, purple to violet compound head terminating each branch. Each small head contains a few peripheral female florets and central bisexual florets with tubular corollas. The fruit is a minute, oblong cypsela lacking a conspicuous pappus.
The genus Sphaeranthus is distinctive within tribe Inuleae for its glomerulate, second-order capitula, and S. indicus is its most familiar and economically significant species, valued throughout South Asia in Ayurvedic and folk medicine for its essential oils and bioactive sesquiterpenoids and flavonoids. Ecologically it behaves as a pioneer of disturbed, periodically inundated soils and is locally abundant; it is of least conservation concern and indeed often regarded as a ruderal weed across its pantropical range.
Author: Gaertn. · Sources: POWO (Kew), GBIF, Flora of China, Flowers of the Himalaya, Annotated Checklist of the Flowering Plants of Nepal, Anderberg monograph of tribe Inuleae