Potamogeton L.
Characters of the family. All or most lvs alt. and all stipulate. Cosmopolitan. Nearly 100 spp.; only 1 of the 4 N.Z. spp. likely to be endemic.
Key
2
Lvs all grasslike, parallel-sided, with ∞ close, fine longitudinal nerves (occ. obscure); stipules fibrous
Lvs, most or all, elliptic to broadly oval, longitudinal nerves well separated; stipules not fibrous
3
Floating lvs mostly broad-oval and quite obtuse, nerves on each side of midrib not > 6; submersed lvs narrow-elliptic, ± translucent; achenes flattened and 3-keeled when dry, green to brown
Floating lvs mostly broad-elliptic and subacute, nerves on each side of midrib us. 6 or more; submersed lvs, if any, not differing greatly in shape and texture; achenes swollen and not obviously 3-keeled, often reddish
The present account is based largely on the work of Miss R. Mason who has studied the genus in N.Z. over many years. She has been unable to confirm earlier records of several N. Hemisphere spp. in N.Z. (see Bull. Wellington bot. Soc. No. 21, 1949, 12); examples are: P. gramineus (for P. ochreatus?); P. heterophyllus (for P. cheesemanii?); P. polygonifolius and P. natans (for P. suboblongus?).
![Fig. 2. POTAMOGETON. P. cheesemanii : floating leaf, submersed leaf, fruit. P. suboblongus : floating leaf; fruit. P. ochreatus : leaf-tip; leaf-base with free fibrous stipule. P. pectinatus : leaf-tip; leaf-base with adnate stipule; swollen rhizome-buds; portion of inflorescence. © All rights reserved. [Image: 4X2B]](https://data.landcareresearch.co.nz/Image/4X2B/SysPortalPreview)
Fig. 2. POTAMOGETON. P. cheesemanii : floating leaf, submersed leaf, fruit. P. suboblongus : floating leaf; fruit. P. ochreatus : leaf-tip; leaf-base with free fibrous stipule. P. pectinatus : leaf-tip; leaf-base with adnate stipule; swollen rhizome-buds; portion of inflorescence. © All rights reserved. [Image: 4X2B]
