Ecology of Desert Plants. I. Observations on Germination in the Joshua Tree National Monument, California

Abstract

Observations on the germination of desert plants in the Joshua Tree National Monument and surroundings have shown that plants can be divided into 5 groups as far as their germination and growth are concerned: 1. Summer annuals (Amaranthus fimbriatus, Boerhaavia spicata, Bouteloua aristidoides, Bouteloua barbata, Euphorbia micromera, Euphorbia setiloba, Mollugo Cerviana, Pectis papposa, Portulaca oleracea), which only germinate after heavy summer rains. 2. Winter germinating spring annuals (Cryptantha, Eriophyllum Wallacei, Filago, Gilia species, Nemacladus, Pectocarya, Plantago, etc.), most of them of diminutive size, germinating almost exclusively after late fall and winter rains. 3. Summer germinating spring annuals (Abronia, Erodium cicutarium, Oenothera deltoides, Salvia Columbariae, etc.) to which most of the larger-sized spring annuals belong. 4. Plants unrestricted in germination conditions (Cucurbitaceae, Datura, Palafoxia linearis) which can be found as seedlings at almost any time of the year after rains. 5. Shrubs. These are almost all summer germinators (Acacia, Chilopsis, Dalea, Fouquieria, Hymenoclea, Hyptis, Larrea, Lycium, etc.) with the exception of Eriogonum which germinates only in winter. These observations explain in general the distribution in time and space of the desert plants in the Joshua Tree National Monument.