Bolander’s quillwort (Isoetes bolanderi) COSEWIC assessment and status report: chapter 8
Biology
Isoetes bolanderi develops slowly, the plant resulting from the joining of a microspore and megaspore on the lake bottom. Microspores and megaspores mature by late summer and are released into the lake bottom environment when the leaves decay in late summer or early fall. Leaves apparently do not persist over winter, with the plant dying back to the corm top each autumn. This species grows in extensive, sometimes rather dense stands.
Isoetes bolanderi is a sexual diploid that produces viable spores. Apogamy has not been detected in North American Isoetes (Brunton and Taylor 1990, Brunton and Britton 1999) nor are other forms of vegetative reproduction known in North American aquatic Isoetes (Kott and Britton 1983, Taylor et al. 1993). Isoetes bolanderi likely requires 3-5 years to mature sufficiently to produce viable microspores or megaspores. The longevity of mature plants is unknown but other North American Isoetes have been maintained in cultivation for 10 to 15 years (W.C. Taylor, pers. comm.). The length of time that free-floating Isoetes spores are viable is unknown but is expected to be considerable. Megaspores apparently containing intact and fluid contents have been observed on Isoetes herbarium specimens dating back to the late 19th century (D. Brunton, pers. obs.).
The Summit Lake population is currently producing new plants as indicated by the substantial number of very small plants with two to four leaves and immature (or no) sporangial development.
Plants in Summit Lake occasionally have been uprooted by moose (Alces alces) feeding (Brunton 1994; C. Smith, pers. comm. 2003) but this does not appear to be a major impact. Such impacts are apparently localized and the movement of whole leaves may redistribute I. bolanderi along the lakeshore.
Barrow’s Goldeneye (Bucephala islandica), bottom-feeding waterfowl which may also contribute to uprooting quillworts, have been observed feeding in Summit Lake (Brunton 1994).
No information known.
Spore dispersal in late summer and autumn occurs with rupture of the sporangium, either by physical impact or by decay. The frequency of dense stands suggests that spores are typically dispersed only a short distance
Shorebirds may unintentionally transport the spores of Isoetes on their feet. Spotted Sandpipers have been observed at Summit Lake (pers. obs) but migratory shorebirds are unlikely to use the area regularly. Large wading animals, such as moose, could carry spores during travel or feeding activity. Dispersal of whole plants could also occur by waterfowl, such as Barrow’s Goldeneye.
Isoetes plants are readily transported by water currents and many I. bolanderi plants were noted floating along the shores of Summit Lake (Brunton 1994) and in its outlet stream (C. Bradley, pers. comm.).
Long-distance dispersal of Isoetes bolanderi spores can be inferred from its geographic distribution pattern, which contains some large gaps. This process is not well understood and the agents and frequency of dispersal are not clear. Given this, it seems highly unlikely that the rescue effect – re-establishment in Canada by naturally dispersing I. bolanderi plants from US populations if the Canadian population should be extirpated – would occur.
A diversity of other aquatic plant species occur with Isoetes bolanderi and share many of its life history characteristics. Since Isoetes species tend to be poor competitors, they are quickly replaced by more competitive species (e.g. Potamogeton spp., Ceratophyllum spp.) when organic matter and nutrient levels are increased. The Isoetes bolanderi population at Summit Lake has few other associated species (Brunton 1994, Smith and Bradley 2003).
Isoetes bolanderi is associated with high water quality and limited competition from other aquatic species. Other aquatic quillwort species have been eliminated from large areas of their former range in eastern North America as a result of their inability to respond to such changes (Brunton 2000) and a similar sensitivity can be expected for I.bolanderi.
While emergent Isoetes species can be maintained in cultivation for prolonged periods (9+ years), aquatic species are more difficult to cultivate, likely due to their cold temperature requirements. Isoetes bolanderi plants from Wyoming were successfully maintained in cultivation for less than two years (D. Brunton, pers. obs.).
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