Origin and nature of vessels in monocotyledons. 6. Hanguana (Hanguanaceae)

Vessel elements from macerations of roots and stems of Hanguana malayana were studied with scanning electron microscopy (SEM). Vessel elements are present in both stems and roots. The vessel elements of roots are slightly more specialized than those of stems in having greater differentiation of perforation plates from lateral wall areas. Long areas of transition between lateral wall areas and perforation plates, consisting of 10 or more pits (arguably perforations) with porose membranes or threadlike pit membrane remnants, characterize vessel elements of both stems and roots of Hanguana. Tracheids may be present, but cannot be identified with certainty. The vessel elements of Hanguana are like those of Acorus (Acoraceae) in primitiveness and are among the most primitive recorded for monocotyledons. These facts are consistent with placement of Hanguana in a monogeneric family, rather than in Flagellariaceae or any other family of monocotyledons.