Tracheid

From Palaeos

This definition used to be so simple. Its like this. In the good old days, xylem had two kinds of tube-like systems, vessels and tracheids. Vessels were wide, open, short and dead. Tracheids were narrow, closed-ended, long, and mostly had some living cell associated with them. Then came Carlquist & Schneider (2002). These folks unfairly used actual observations, rather than generations of classroom dogma. This was an utterly rotten thing to do because it messed up a lot of perfectly good, if slightly faded, lecture notes. C&S pointed out that there are at least six character states involved, and that any given plant may have tubular things of several different kinds falling almost anywhere in that morphospace. To complicate matters further, in plants with vessels, the tracheids may have specialized as structural support tissues (biological rebar). In plants without vessels, tracheids often differ strongly between vessel-like earlywood and latewood tracheids. The morphological characters identified by C&S are shown in the figure.

References

Carlquist, S & EL Schneider (2002), The tracheid–vessel element transition in angiosperms involves multiple independent features: cladistic consequences. American Journal of Botany 89: 185-195.

Credits

ATW?