Rotala ramosior (L.) Koehne
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Basis for Listing
Rotala ramosior has a wide distribution in eastern and central North America but does not have a wide distribution in Minnesota. It is presently known only from shallow wetlands associated with small ponds in northern Anoka County. Many of the known R. ramosior sites have not been seen since 1945 and are located in what is now the Twin Cities metropolitan area. Most of these populations have presumably been destroyed by subsequent urban and agricultural expansion. Many of the remaining habitats are in areas projected to experience similar development in the near future. The comparatively recent invasion of aggressive non-native plant species is also taking a heavy toll on wetland habitats. It seems plausible that undiscovered populations may exist elsewhere in the region, especially considering that this species is small and easily overlooked, even by experienced botanists. But all evidence supports the conclusion that this is a very rare species requiring special conservation action if it is to survive in Minnesota. Rotala ramosior was listed as a threatened species in Minnesota in 1996.
Rotala ramosior is the only member of its genus in Minnesota and can be identified easily when in flower or fruit. However, the species is quite inconspicuous and may be difficult to detect in its chosen habitat. It is a low plant with a simple or diffusely branched stem. Leaves are small, petioled (sessile in var. interior), opposite, entire, and without stipules. Flowers occur singly in leaf axils. The calyx has 4 short lobes with appendages in each sinus and encloses a 4-locular, many-seeded capsule. Four pink petals are small and promptly deciduous. There are 4 stamens and 1 style, which has a capitate stigma.
The populations of R. ramosior in Minnesota typically occurred on the sandy shores of small, shallow lakes set in a savanna landscape. Such shorelines undergo seasonal fluctuations that expose broad beaches in late summer, to the apparent benefit of this species. Habitats of this type were once common on the flat, sandy, outwash plain of the Twin Cities metropolitan area, but they rarely developed elsewhere in the state. Because these lakes were small and shallow, they were easy to fill, especially in an era when protecting wetlands was not a priority. Now, such lakes with undisturbed shorelines and native vegetation are a rarity.
Biology / Life History
Rotala ramosior is a small, inconspicuous annual (Gleason and Cronquist 1991). It appears to experience population booms and busts that may be related to water level fluctuations on its shoreline habitat. It has dimorphic or trimorphic flowers and styles and stamens of various lengths, thus helping to ensure cross-pollination (Voss 1985).
Conservation / Management
Habitat destruction or degradation seems to be the biggest threat to R. ramosior. The lakeshore and pond margin habitat required by this species is in high demand for a variety of uses. It is especially vulnerable to the draining and filling activities that typically precede industrial development. Residential, commercial, and recreational developments are also claiming potential habitat and contributing to the general decrease in populations of this species. Also, these ponds are sometimes used for stormwater retention, or may be dredged to provide habitat for waterfowl. This decline is severe in the face of the rapid urban and suburban growth of the greater Twin Cities area. It is critically important to identify high quality examples of this habitat type and take measures to ensure their protection.
Conservation Efforts in Minnesota
No specific conservation efforts have been undertaken on behalf of this species.