Dehiscence

Day 346: Here's a good word for you to drop into the conversation at the next party you attend: dehiscence. Of course, if your party companions are the same kind of people I enjoy being around, no one will bat an eye, but that's another subject. The term comes directly to us from the Latin verb "dehiscere," "to split open or gape," which is exactly what certain seed pods do when ripe. Legumes are notorious for their ability to dehisc violently when fully dry, often throwing seed 25 feet or more from the parent plant. Others such as the slender siliques of Fireweed simply split and peel backwards to release their fluff into the breeze. On the other hand, indehiscent fruits such as sunflower seeds and acorns open only when the germinating seed begins to exert pressure from inside, or when the hard outer shell is weakened by some external factor (freezing, fire, moisture, etc.). In the case of Fireweed (Chamaenerion angustifolium, shown here), the teensy-tiny seed attached to the silky pappus is so hard that it still requires scarification by fire before it can sprout. It is often the first plant to emerge in clear-cut timber plots which have been burned over to remove debris. But do not assume that fluff and dehiscence equate. They do not. Although Fireweed siliques dehisc to release their seeds, the common dandelion is indehiscent, its fruit an achene, albeit attached to a silken parachute.