Seed germination inAcaciaspecies and their relation to altitudinal gradient in south-western Saudi Arabia

Seed germination ofAcaciaspecies found in south-western Saudi Arabia responded in three different ways to temperature: (1) Germination over a broad range of temperature (between 10 and 40°C) was recorded inAcacia asak, A. ehrenbergiana, A. iragensis, A. hamulosaandA. tortilisssp.spirocarpa. (2) Cold-evading germination (between 20 and 40°C) was recorded inA. oerfota. (3) Heat-evading germination (between 10 and 35°C) was recorded inA. origena. Plants of the first two types were found in desert to semi-desert environments between sea level and 2000 m, whereas, plants of the third type occur in a cool temperature environment between 1750–2500 m. A strong correlation exists between seed germination, temperature, water and thickness of seed coat.