Wuchsformuntersuchungen im Páramo Costa Ricas: IV. Untersuchungen an Senecio- und Hypericum-Arten

Abstract

Summary Development and growth forms of three species of Hypericum, H. caracasanum, H. irazuense and H. strictum, and two species of Senecio, S.firmipes and S. andicola, are investigated. These species and Chusquea subtesselata, Buddleja nitens and several Ericaceae form constituent elements of the paramo-vegetation of Costa Rica, where the environmental conditions are characterized by diurnal climate, sometimes with nocturnal temperatures below zero and occasional hard winds. Hypericum irazuense and H. caracasanum as well as both Senecio species form shrubs, H. strictum forms shrublets. As typical for shrubs they all show a principally basitonic ramification, which usually takes place at a very early stage of their ontogeny. The more or less vigorous branches themselves, however, show an acrotonic ramification, since after the anthesis of the terminal flower or inflorescence, or even during anthesis, innovation shoots continuing the ramification system start to arise from the rudls of leaves below the terminal flower or inflorescence and soon overtop the relative main shoot. The number of these continuing branches often increases during lifetime causing an increasing density of ramification towards the periphery of the shrubs. By this manner globe shaped or hemispherical shrubs with a dense peripheral mantle of green innovation shoots are formed. This is especially true for Hypericum irazuense and Senecio firmipes, while ramification in S. andicola is less dense. This growth form, as well as anatomical features of the leaves, appear to be well adapted to a reduction of transpiration. In Hypericum caracasanum, however, the acrotonic ramification of the basal branches is restricted to small numbers of secondary and tertiary branches and instead of forming a globe-shaped or hemispherical shrub the larger branches, which bear leaves only on their very distal parts, remain relatively solitary. Probably due to this architecture the plant is usually found in sheltered conditions. On the other hand the growth form of Hypericum strictum, which can apparently grow on poor soil in very exposed and occasionally dry habitats, is quite variable. The plant, which in sheltered places usually forms hemispherical or treelet-like dwarf-shrubs, can develop tuft-like or broom-like shrubs. The upright position of its epistomatic leaves could be an effective protection against strong wind. Under unfavourable conditions the growth form of Hypericum irazuense also can be modified by continual vegetative development of major branches. Senecio firmipes can also develop tillers (root suckers).