Ogden's Pondweed (Potamogeton ogdenii) COSEWIC assessment and status report: chapter 3

• Previous page
• Table of contents
• Next page

Species Information

Name and classification

Ogden’s pondweed was first described in 1983 based on a 1970 collection by Robert Haynes and Stanley Smith in Columbia County, New York (Hellquist & Hilton, 1983). In 1970, the plants were thought to be Potamogetonx longiligulatus, then considered to be a hybrid between P. strictifolius and P. zosteriformis (Hellquist & Hilton, 1983). Later work placed P. x longiligulatus in synonymy under P. strictifolius (FNA, 2000). The hybrid between P. strictifolius and P. zosterformis should be called P. x haynesii (Hellquist & Crow, 1986). Further study of the Columbia County material resulted in the plants being described as a new species, Potamogeton ogdenii, that had probably originated as a hybrid between P hillii and P. zosteriformis (Hellquist & Hilton, 1983). Its treatment as a distinct species has been accepted in recent treatments, such as Gleason & Cronquist (1991) and FNA (2000).

Description

Ogden’s pondweed is a submerged, annual, aquatic plant with freely branching stems that are compressed-filiform and rigid. The leaves are green to greenish-brown, 5-7 cm long and 3-9 nerved (Hellquist & Hilton, 1983). The leaf apex is cuspidate to aristate, 1.2-2.9 mm wide with 1-2 rows of lacunae (air cells) on each side of the leaf midrib. The leaf-like stipules are brown and slightly fibrous with a partially shredded tip. Fruits are only occasionally produced and occur in cylindric spikes 5-11 mm long with 2-4 whorls. Each orbicular fruit is dark green and 2.2-3 mm across. Winter buds (turions) are uncommonly produced (Hellquist & Hilton, 1983) but appear to be the most common method of reproduction (Hellquist & Mertinooke-Jongkind, 2003). The turions can be produced terminally or laterally and are 37-92 mm long and 26-60 mm wide with ascending outer leaves. In many cases, the winter buds are undifferentiated leaves crowded together (Hellquist & Hilton, 1983). Rhizomes aren’t produced; however, the plant can perennate from fragments (Hellquist & Hilton, 1983). Line drawings can be found in Crow & Hellquist (2000), Hellquist & Hilton (1983) and Holmgren (1998).

Ogden’s pondweed belongs to sub-section Pusilli of the genus Potamogeton. This sub-section is made up of the linear-leaved pondweeds, including P. confervoides, P. zosteriformis, P. hillii, P. foliosus, P. friesii, P. strictifolius, P. ogdenii, P. obtusifolius, and P. pusillus. Due to their close vegetative similarity and morphological variability, members of this group are difficult to identify without flowers or fruit (Haynes, 1974). P. confervoides is distinctive with its branching leaf clusters alternating along the stem. P. zosteriformis has flattened stems 2 mm or more in width. P. hillii has flowering/fruiting peduncles that are mainly axillary. P. foliosus has elongate rhizomes and spikes with only 1 or 2 whorls of flowers or fruit. P. freisii has rounded leaf tips and turions with outer leaves at right angle to the inner leaves. P. strictifolius has white stipular sheathes and leaves that are usually 3 to 5-veined. P. obtusifolius has non-fibrous stipular sheathes and leaves up to 3.5 mm wide. P. pusillus has non-fibrous stipular sheathes and fruits 1.5 to 2.2 mm across. Although the genus Potamogeton has historically been divided into several sections and subsections, Haynes and Hellquist, authors of the Flora of North America treatment of the genus (FNA, 2000), do not believe that recognition of infrageneric categories is warranted. In vegetative condition, Ogden’s pondweed is also very similar to non-flowering plants of water stargrass (Zosterella dubia). The latter lacks the prominent midvein that is found on leaves of the genus Potamogeton.

Fruiting or flowering specimens of Ogden’s pondweed can best be identified using keys and/or illustrations in Gleason & Cronquist (1991), Hellquist & Hilton (1983), Hellquist & Crow (1986), Crow & Hellquist (2000), Hellquist & Mertinooke-Jongkind (2003), Holmgren (1998), or FNA (2000).

Genetic description

No specific genetic information was found for this globally rare species.

Designatable units

The species is treated as a single designatable unit.