| MadSci Network: Botany |
Generally, you would expect the tumbleweed to be dead or mostly dead when it is tumbling, although the seeds it carries would be alive. There are several reasons why you would expect tumbleweeds to be dead while they are tumbling. 1. Tumbleweed (Salsola kali) is an annual, and annuals die after producing seed. 2. Tumbleweed would not tumble as well if it was alive and therefore heavier because living tissue contains a lot more water than dead tissue. 3. Some types of tumbleweed also curl into a ball better as they dry. This curling into a ball when dry is easily demonstrated with the resurrection plant (Selaginella lepidophylla) which is a ball shape when dry but opens into a flat circle when wetted. 4. Tumbleweeds are usually brown but plants are usually green when alive and brown when dead. References Tumbleweed Why must the tumbleweed tumble? Resurrection plant dry and wet Living Salsosa kali photo
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