Assessment of availability, ecological feature, and habitat preference of the medicinal herb Houttuynia cordata Thunb in the Brahmaputra Valley of Assam, India.

Houttuynia cordata Thunb. is a rhizome-bearing aromatic medicinal herb and is restricted to specialized moist habitats. The plant is collected from natural habitats for local consumption and trade. The status of the species and its variations in physiological performance in different habitats were studied in selected sites of geographically different areas of Brahmaputra valley in eastern India. The surveys were conducted in two different growth stages of the plant during 2005-2007. The sites where the species was encountered were marked and a distribution map was prepared. The frequency and density of the plant was higher in the moist habitats with higher organic carbon (0.85+/-0.05%). Generally, the density, biomass production and growth had significant (P<0.05) positive relationship with the soil physicochemical properties (linear curve fit). Soil moisture was the most dependent factor for the plant growth and the optimum growth was recorded at 78+/-5.6% (r2=0.9; P<or=0.01). The physiological performance of the plant in all the studied sites were significantly varied (P<0.05). The growth and development of H. cordata were also different in the flowering and senescence stages. Clay loam soil, average soil pH of 5.9, and 78% soil moisture were the favorable soil characteristics for the better growth of H. cordata and, hence, these data may be considered for conservation of the species.