You selected Najas flexilis var. robusta Morong. This is a synonym for:

Accepted scientific name:
Najas flexilis (Willd.) Rostk. & W.L.E.Schmidt (accepted name) 1 literature reference for Najas flexilis (Willd.) Rostk. & W.L.E.Schmidt
Synonyms:
Caulinia flexilis Willd. (synonym) 1 literature reference for Caulinia flexilis Willd.
Fluvialis flexilis (Willd.) Pers. (synonym) 1 literature reference for Fluvialis flexilis (Willd.) Pers.
Najas caespitosus (Maguire) Reveal (synonym) 1 literature reference for Najas caespitosus (Maguire) Reveal
Najas canadensis Michx. (synonym) 1 literature reference for Najas canadensis Michx.
Najas flexilis subsp. caespitosus Maguire (synonym) 1 literature reference for Najas flexilis subsp. caespitosus Maguire
Najas flexilis var. microcarpa Nilsson (synonym) 1 literature reference for Najas flexilis var. microcarpa Nilsson
Najas flexilis var. robusta Morong (synonym) 1 literature reference for Najas flexilis var. robusta Morong
Common names: -
Classification:
Plantae
Phylum Magnoliophyta
Class Liliopsida
Order Alismatales
Family Hydrocharitaceae
Genus Najas
Distribution: Temp. Northern Hemisphere
Additional data: -
Source database: World Checklist of Selected Plant Families, 27 Nov 2009
Latest taxonomic scrutiny: Govaerts R., 06-Jan-2005
Online resource: http://apps.kew.org/wcsp/namedetail.do?accepted_id=308239&repSynonym_id=-9998&name_id=308239&status=true
CoL taxon LSID: urn:lsid:catalogueoflife.org:taxon:f0c4cc62-29c1-102b-9a4a-00304854f820:ac2010