Potamogeton vaseyi J.W. Robbins
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Basis for Former Listing
Potamogeton vaseyi is an aquatic macrophyte that inhabits small, softwater lakes in the northeastern portion of North America. It is reported to be an uncommon species across its range (Haynes and Hellquist 2000), but it seems to be especially uncommon in Minnesota, where it reaches the very western edge of its range. Several threats to the species' habitat have been identified including declining water quality, which seems to be a statewide trend, and the accelerating invasion of non-native species, which seems to be a worldwide trend. Potamogeton vaseyi was listed as a special concern species in Minnesota in 1984.
Basis for Delisting
Recent botanical searches by the Minnesota Biological Survey discovered P. vaseyi in just over 100 lakes of more than 1,500 lakes that were surveyed. It is now known to be more common and widespread than once thought to be. Special concern status is no longer necessary, and Potamogeton vaseyi was delisted in 2013.
Potamogeton vaseyi is a rooted, aquatic plant that produces small floating leaves when fertile, but remains submerged if sterile. The blades of the submerged leaves are linear-filiform in shape, 2-8 cm (0.8-3.1 in.) long, and 0.1-1 mm (0.004-0.04 in.) wide. The margins are entire, and the apex is acute to almost bristle-tipped. Lacunae (apparently empty or transparent cells) are usually present in 1 or 2 rows on each side of the midvein. The stipules are persistent but inconspicuous; the margins are convolute, free from the blade, and 0.4-1.2 cm (0.2-0.5 in.) long. The petiole of the floating leaves is 5-25 mm (0.20-0.98 in.) long; the blade is elliptic, spatulate or obovate in shape, 0.6-1.5 cm (0.2-0.6 in.) long, and 3-8 mm (0.12-0.31 in.) wide. The base of the blade is acute, and the apex is obtuse; there are 5-9 veins on the surface. Turions (winter buds) are common in the axils, and are 0.5-2 cm (0.25-0.75 in.) long and 0.5-1.2 mm (0.020-0.047 in.) wide. The inflorescence is 5-30 mm (0.20-1.18 in.) long; it is held above the surface in flower and becomes recurved in fruit. The fruits are sessile, obliquely round-obovoid in shape, keeled abaxially, 1.5-2.5 mm (0.06-0.10 in.) long, and 1.2-1.6 mm (0.05-0.06 in.) wide, with an erect beak 0.3-0.5 mm (0.012-0.020 in.) long. The submerged leaves of P. vaseyi are very similar to those of P. pusillus (very small pondweed), a common species, and the two plants often grow intermixed. The leaves of P. vaseyi tend to be slightly narrower or finer than those of P. pusillus, but sterile specimens of either species can easily be mistaken for each other.
Water chemistry data are available for 74 of the Minnesota lakes where P. vaseyi has been found. The total alkalinity of these lakes ranges from 1-84 ppm, with a mean value of 30 ppm. The pH ranges from 5.9-9.2 for a mean of 7.5. The size of the lakes (excluding 2 very large reservoirs) averages 22 ha (54 ac.). The most common aquatic plant species associated with P. vaseyi include Nuphar variegata (bullhead pond-lily), Nymphaea odorata (American white waterlily), Najas flexilis (flexuous naiad), P. pusillus, Utricularia vulgaris (common bladderwort), Eleocharis palustris (marsh spikerush), P. amplifolius (largeleaf pondweed), P. epihydrus (ribbonleaf pondweed), P. spirillus (coiled pondweed), Brasenia schreberi (watershield), and Vallisneria americana (American eelgrass).
Biology / Life History
Very little is known about the biology and life history of P. vaseyi, or why it is rare. It is a rooted, aquatic plant that reproduces by seeds and turions (winter buds). Turions are excellent modes of vegetative reproduction. The structures are produced at the stem tips and eventually fall to the substrate, either by a portion of the stem breaking off or by the stem itself falling to the substrate. The turions survive an unfavorable season, germinate, and then grow into new plants during the next growing season. Because the unfavorable season is usually winter in North America, turions have been called "winter buds" (Haynes and Barre Hellquist 2000).
Conservation / Management
Established populations of P. vaseyi should have no trouble maintaining themselves as long as the lake habitats that support them remain unimpaired. Impairment, of the type that could threaten aquatic plant populations, usually results from contamination by agricultural or industrial chemicals, faulty or poorly designed septic systems, poor municipal storm water management, and/or loss of filtering capacity when native shoreline vegetation is removed. The harmful consequences of impairment usually include reduced water clarity, warming, and increased competition from non-native, invasive species.
Conservation Efforts in Minnesota
No known conservation efforts have been undertaken specifically on behalf of P. vaseyi. However, the DNR's Shoreland Habitat Restoration Program is working to expand the diversity and abundance of native aquatic and shoreland plants, to improve and protect the quality of shoreline habitat, and to enhance and protect water quality in Minnesota's lakes and streams. To achieve this goal, the program conducts site visits, provides planting, restoration, and management recommendations, and offers cost share funding to watershed districts, conservation organizations, lake associations, private citizens, and local units of government.