This sounds like a big project. First, you would need to know which species have been recorded from Sri Lanka and surrounding regions. Then, with a list of relevant species of the region, you would have to look for the original descriptions of these species; often, the type repositories are mentioned there. For older publications, the search for types may be a little more difficult. If you know where the types are deposited, you may either look online for photographs [some collections make them available], or would have to approach the curators of the institutions.

Besides, you may wish to search for revisions, field guides, checklists etc. of species in the Indian Ocean, which may give additional hints.

I would also suggest to consult the International Code of Nomenclature for Algae, Fungi, and Plants (Melbourne Code) of July 2011, for nomenclatural rules and rules of typification, which is available online:

http://www.iapt-taxon.org/nomen/main.php

Dear Sir,

Thanks very much for your valuable insight for this.

Dear Mr. Kaluthota,

Thanks very much for your information and I have  visited several time to NH, but It dose not have good collection for seagrass. Thanks verymuch for your valuble information.