First investigation of seasonal changes in the ecological and anatomical traits of Launaea sarmentosa (Willd.) Kuntze (Compositae) on the Andaman coasts, Thailand

Launaea sarmentosa (Willd.) Kuntze, a creeping herb native to the Andaman coasts of Southern Thailand, faces significant threats from habitat loss and environmental changes following the 2004 tsunami. This study investigated its ecological and anatomical characteristics across four coastal sites in Phuket and Phang-Nga Provinces. Sampling was conducted during the rainy season (November 2023) and the dry season (April 2024). Results revealed shoot density and below-ground fresh weight were highest during the rainy season and at moderately sunny sites. The chlorophyll a / b ratio varied between seasons and sites, while the total chlorophyll/carotenoid ratio differed between sites but not seasons. Leaf anatomical features showed significant seasonal differences. Epidermis (upper and lower), mesophyll thickness, and upper epidermal cell area were greater during the dry season, but lower epidermal cell area showed no variation. In upper-layer soil, chloride content varied by season, while sand, clay, magnesium, and pH differed between sites. In lower-layer soil, sand, silt, chloride, and magnesium varied seasonally, while nitrogen, phosphorus, and calcium differed by site. Climatic variables also varied; air temperatures were lower, and relative humidity was higher during the rainy season, with the coolest, most humid conditions at moderately sunny sites. In summary, the favorable conditions of L. sarmentosa likely include moderately sunny environment, humid soil, and a high clay content, which were associated with higher shoot density and biomass, emphasizing the importance of seasonal and site-specific factors in promoting the growth and survival of L. sarmentosa in natural populations.