Amphicarpum, native in the southeastern United States, has fertile cleistogamous spikelets on filiform runners at the base of the culm, those on the terminal panicle are sterile.
Lankester (5) has shown (and his views have been accepted by Professors Korschelt and Heider in their treatise on Embryology) that the limb of the lowest Crustacea, such as Apus, consists of a corm or axis which may be jointed, and gives rise to outgrowths, either leaf-like or filiform, on its inner and outer margins (endites and exites).
The rami may be flattened for swimming, when it is " a bi-ramose swimmeret," or both or only one may be filiform and finely annulate; this is the form often presented by the antennae of Crustacea, and rarely by prae-oral appendages in other Arthropods.
In unisexual flowers it is not uncommon to find vestiges of the undeveloped stamens in the form of filiform bodies or scales.
The filament is usually, as its name imports, filiform or threadlike, and cylindrical, or slightly tapering towards its summit.