The correct citation for the entire website is:
Torke, B. M. and Mansano, V. F. (editors). January 1, 2011-onward. The Swartzia Pages (https://sweetgum.nybg.org/science/projects/swartzia). The New York Botanical Garden, Bronx, NY.
To cite individual pages in the website use the format in the following example:
Torke, B. M. Swartzia nicaraguensis In: Torke, B. M. and Mansano, V. F. (editors). January 1, 2011-onward. The Swartzia Pages (https://sweetgum.nybg.org/science/projects/swartzia). The New York Botanical Garden, Bronx, NY.