Comparative Anatomy and Phylogeny of the Casuarinaceae

Abstract

1. The chief purposes of this investigation have been to contribute toward a better understanding of the evolutionary status of the Casuarinaceae; to present a thorough anatomical description of the family; and to tabulate, at least provisionally, the outstanding characteristics of twenty-nine species. 2. The anatomy of the secondary xylem of the old wood (wood at some distance from the pith) may be summarized as follows: Growth rings are poorly defined or absent; both tracheids and fibertracheids are found in all but one species, in which only tracheids occur; tracheids generally predominate, and the larger, thinner-walled tracheids are vasicentric; the fiber-tracheids often have very thick walls; the fibrous elements are extremely short to moderately long, mostly short to medium-sized; spiral thickenings occur in the fibrous elements of six species. The range of species means for the number of vessels per square millimeter is from moderately few to very numerous; vessel distribution is universally solit...