Several unexpected observations were made recently while collecting plants of Stylites E. Amstutz for anatomical study. The plants were collected near the end of the growing season (18-19 April 1979) so as to obtain young plants which had just completed various numbers of growing seasons. In the type locality, Stylites is described as forming pure colonies which stand just above the water level in the lacustrine bog in which they are found (Rauh & Falk, 1959); but the plants we collected at 4100 m altitude (Karrfalt & Hunter 22, NY) near Lago Junin, 14 km north of Junin, Peru, were invariably growing in association with various flowering plants (Figs. 1 and 2) and were frequently submerged. The colonies at the Junin locality were generally in the form of radially symmetrical, dome-shaped hummocks (Fig. 1), but various other rounded shapes occurred as well. The hummocks ranged in diameter from 20 to about 200 cm. The larger hummocks generally were found to contain a larger proportion of other plants in addition to Stylites than did the smaller ones. The plants in the hummocks were extremely densely packed and usually stood above the water level, but some hummocks were partially or completely submerged. The submerged portions of these hummocks were populated nearly exclusively by Stylites, but the emergent portions included other plants as well (Fig. 5). These plants usually were rather small (with stems a few millimeters in length), but some were quite good-sized (stems 2-4 cm long) and bore about 40 leaves up to 7 cm long, as well as numerous gemmae. Their leaves did not have the typical flattened form with deflexed tips, but rather were subtriangular to terete in cross section and ascending. All intermediate forms between these atypical leaves and those described by Rauh and Falk (1959) were also seen; the variation in leaf morphology will be described in detail in a subsequent report. The plants with the atypical leaf form always were submerged and not densely crowded. On the other hand, plants bearing typical leaves occurred both above and below the water level in the bog, but these plants always were densely crowded. Leaf form correlates with population density rather than with emergence or submergence. The nature of this correlation is not certain, but experiments in progress suggest that it is largely or entirely environmental. In contrast to its very limited geographical range, Stylites is extremely vigorous and abundant where appropriate conditions for its growth exist. The Junin locality is a bog which has been used as a pasture for many years. It is heavily grazed by sheep and llamas, as indicated by the cropped herbage (Figs. 1 and 4) and abundant llama dung. The Stylites plants, however, very rarely show any evidence of even accidental damage by the animals. The Junin locality occupies at least several acres; we were unable to determine its full extent due to our anoxemia and consequent lack of energy. The leaves of Stylites are coated with considerable quantities of mucilage, as are the basal parts of the leaves of all Isoetes species of which we have seen living
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Mar 1, 1992
Josef Senn + 3
Open Access
