Wuchsformuntersuchungen im Páramo Costa Ricas III. Untersuchungen an Ericaceen-Arten

Abstract

The growth forms of 5 species of Ericaceae which are widely distributed in the Páramo vegetation of the Cordillera de Talamanca (Cerro de la Muerte) in Costa Rica were analyzed. All of them are shrubs with fundamentally basitonic ramification, but acrotonic ramified branches. Comarostaphylis arbutoides grows on rocky sites forming vigorous, sometimes treelike shrubs up to 4 m height, often with a somewhat spherical contour. The primary axis often continues growth for several years before the first branches are developed. When the main shoot has reached a certain size the terminal bud dies off and the primary shoot can be continued by distal branches. Sooner or later the ramification system of the primary axis is completed or even replaced by the development of basal branches which ramify in an acrotonic way as well. Later they also can be replaced by more vigorous basal branches. The acrotonic mode of ramification of the branches is frequently repeated, resulting in a dense arrangement of branches towards the periphery of the shrub. This way of branching can be supported by shoots originating at the base of the plant in a more or less early stage of development. Only the renewals of the last two vegetation periods bear green leaves. Maturity is reached after 10 to 15 years. The terminal inflorescences form (polytelic) heterothetic double racemes. After flowering they are overtopped by renewals arising from the axils of the leaves preceding the inflorescence and repeating the pleiochasial ramification. Under certain conditions (after fire) tillers can be formed. The normally spherical contour of the shrub can be considerably modified under the influence of wind without any change in the mode of ramification. Pernettia coriacea and P. prostrata are dwarf shrubs with an early development of basal branches while the primary axis dies off. The same can happen with the initially developed basal twigs, which are replaced by stronger branches. Notwithstanding the basitonic development of the main branches these show an acrotonic pleiochasial branching. The flowers of both species are developed terminally on uniflorous (monotelic) short shoots. Pernettia prostrata can spread by subterranean stolones to a considerable amount. Vaccinium consanguineum can grow as a low squarrose shrub as well as a man-high bush sometimes assuming a spherical outline. The primary axis dies off after 2 – 4 periods of growth and is overtopped by branches, a large number of which originates from the hypocotylar region. These branches themselves can at first ramify in a basitonic manner as well and then proceede to an acro-mesotonic mode of branching. Flowering plants could be found all over the year. The inflorescences are 8–15 flowered axillary bracteose racemes which for the presence of a series of bud scales must be interpreted as short shoots. Sprouts originating in the larger branches can ramify in the distal third, whereas their terminal part dies off. After damage of the overground parts fast growing tillers can be formed from the basal branches or even from the hypocotylar region. Vaccinium floribundum , a small slowly growing espalier spreads horizontal branches over the rocky ground and shows a high degree of polymorphy in its ramification. It also develops a far reachingdense network of stoloncs closely under the surface of the soil, which produces vertically growing leafy shoots. In their distal parts these can bear axillary racemes of 3 – 7 flowers. which during a period of rest in the drier season from October to April remain enveloped by bud scales and thus should be interpreted as shorts shoots. Vaccinium floribundum , however, as well as Pernettia prostrata display mainly vegetative propagation by stolones whereas Comarostaphylis arbutoides and Vaccinium floribundum disseminate by berries.