Pennaceous feather Pennaceous feather The pennaceous feather is a type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs. A pennaceous feather has a stalk or quill. Its basal part, called a "calamus", is embedded in the skin. The calamus is hollow and has pith formed from the dry remains of the feather pulp, and the calamus opens below by an "inferior umbilicus" and above by a "superior umbilicus". The stalk above the calamus is a solid "rachis" having an umbilical groove on its underside. Pennaceous feathers have a rachis with "vanes" or "vaxillum " spreading
Acorus calamus asexually. The tetraploid variety is usually known as "Acorus calamus var. angustatus" Besser. A number of synonyms are known, but a number are contested as to which variety they belong. It is morphologically diverse, with some forms having very broad and some narrow leaves. It is furthermore also cytotypically diverse, with an array of different karyotypes. "A. calamus" has been an item of trade in many cultures for thousands of years. It has been used medicinally for a wide variety of ailments, and its aroma makes calamus essential oil valued in the perfume industry. The essence from the rhizome is