Montana Field Guide

Guadalupe Water-nymph is a submerged aquatic annual with slender, branching stems up to about 7 dm long. The opposite, ribbon-like leaves, usually with additional leaves in their axils, are 0.5-2 cm long and have minutely toothed margins and enlarged bases. Tiny unisexual flowers, both male and female on the same plant, are borne singly, without stalks, in the axils of leaves. The male flowers have a single stamen enclosed in a translucent bract which is surrounded by a firmer bract, and the female flowers consist of a single naked pistil. The fruits are single seeded with a thin, papery covering. The long tapered seeds are round in cross-section and are dull and coarsely pitted with 10-20 rows of pits across the middle.

Flowering in July, with mature fruit in August.

Distinguished from other genera of submerged aquatics in Montana by its opposite ribbon-like leaves with expanded bases, usually with secondary leaves in their axils, and also by its solitary, axillary, unisexual flowers. Distinguished from the more common Najas flexilis by having shorter stems, shorter leaves with short tapering tips rather than long tapering tips, and seeds which are dull and coarsely pitted rather than shiny with minute pits.

Guadalupe Water-nymph - Najas guadalupensis, SOC
*Leaves: 5-15 mm long with minutely toothed margins. Ribbon-like with short tapering tips and expanded bases. Additional leaves are often found in the axils. Prickles lacking.
*Seeds: Dull and coarsely pitted, with a honeycomb surface.

Slender Naiad - Najas flexilis, Native
*Leaves: 10–35 mm long with a dilated base that is 2–3 mm wide. From about their mid-section, leaves have a long taper that terminates in a long slender point. Prickles lacking.
*Seeds: Smooth, shiny, and sometimes minutely spotted.

Spiny Naiad – Najas marina, Exotic
*Leaves: Coarsely serrated margins with 8 to 13 teeth on each side of the blade. Prickles can be found on the abaxial (lower) surface of the blade.
*Seeds: Ovoid, reddish brown, and pitted with areoles (outer two coatings of the testa) irregularly arranged, not in distinctive rows or not ladder-like. Seeds are longer than broad with the end walls slightly raised.

Brittleleaf Naiad - Najas minor, NOT DOCUMENTED IN MONTANA
*Leaves: At maturity, blades recurve and become stiff with age. Prickles lacking.
*Seeds: Broader than long and with areoles arranged in longitudinal rows – like the rungs of a ladder.

TAXONOMY
The Najas genus is sometimes placed in the Family Hydrocharitaceae, also known as the Waterweed or Frog’s-bit Family.

Submerged in shallow, fresh waters of oxbow sloughs, ponds, and reservoirs in valleys.

STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).