Small-flowered lipocarpha (Lipocarpha micrantha) COSEWIC assessment and status report: chapter 6
BIOLOGY
General
Several serious conservation challenges are posed by the biology of Lipocarpha micrantha. The annual habit and occurrence in a transient habitat make the location and assessment of viable populations difficult, as detailed below.
Reproduction& Survival
Lipocarpha micrantha is an annual plant. As such it endures conditions unfavourable to growth in the seed stage. After seeds are produced in the fall, the entire population exists only as seed. These seeds will germinate the next time appropriate conditions occur. This may happen in the same location the next summer. However, if conditions are unfavourable for growth, the seeds may not germinate for several years or even decades.
We do not know how long Lipocarpha micrantha seeds may remain viable. Nor do we understand how they are dispersed beyond the observation that they occur in habitats frequented by waterfowl, and in locations where seeds could float to new locations.
As a consequence of the annual habit, Lipocarpha micrantha may persist undetected at locations searched thoroughly by botanists. An unsuccessful search during highwater, when much potential habitat is temporarily unavailable, is therefore not justification for declaring a population extirpated.
This was the case at Pound Net Bay, Ontario, in 2001, where water levels were well above average. When water levels return to average or below this area will provide abundant habitat for Lipocarpha micrantha. The overlooked population may well return from dormant seed, or seed produced by Lipocarpha micrantha populations on the American side of the river.
In contrast, in areas where the habitat has been degraded it is unlikely that Lipocarpha micrantha will persist regardless of water level. This is the case at Holiday Beach, Ontario. Despite favourable low water levels no plants were found. In this case the population is effectively extirpated, as any remaining viable seeds will be unable to germinate.
It is important to note that even in locations where Lipocarpha micrantha has been regularly located, large variation in population size is to be expected between years, and caution should be taken when interpreting long-term trends. Annual species respond dramatically to seasonal variation in growing conditions.
Physiology
The physiological requirements and tolerances of this species are unknown.
Movements/dispersal
Seed may be dispersed by waterfowl or by water. There is some potential for this species to be carried long distances by migrating shorebirds. As a result it may be able to colonize new or historic sites from populations in the United States. This will only be possible for sites where appropriate habitat still exists.
Nutrition and interspecific interactions
Lipocarpha micrantha occurs in sparsely vegetated areas of wet sandy habitats. This is interpreted as a sign that it does not tolerate competition from other plants. It is not found in areas with organic material in the sand (Reznicek, pers. commun., 2001).
Behaviour/adaptability
This species is only found in wet sandy swales and beaches. It is not found on mudflats richer in organic sediment, or drier sandy areas, despite the abundance of these habitats near extant Lipocarpha micrantha populations.