A Study of Stomatal Structure in Pandanaceae 
P. B. Tomlinson 1 
ABSTRACT: Many species of Pandanaceae have unspecialized stomata. In species 
of Pandanus there is a range of stomatal structure involving increasing elaboration 
of papillae arising from subsidiary and neighbouring cells so that guard cells, which 
are otherwise constant in structure throughout the family, are increasingly provided 
with a canopy of papillae which, together with sinking of the stomatal apparatus, 
produces an outer stomatal chamber. In the most specialized stomata this chamber 
is itself virtually occluded by lobed papillae. 
Freycinetia may show significant differences from Pandanus. This linear trend 
of specialization can often be partly or wholly demonstrated on a single individual 
because stomata are always unspecialized on the first scalelike leaves of each renewal 
shoot, thereafter being increasingly specialized on subsequent leaves until the maxi- 
mum potential elaboration characteristic of the species is realised on foliage leaves. 
This is briefly discussed in relation to taxonomy, physiology, and ecology. 
This article is the partial result of a recent 
study of the systematic anatomy of the Pandana- 
ceae in which limited material of all three of its 
genera, Freycinetia, Pandanus, and Sararanga, 
has been examined. Insufficient material has 
been studied to permit worthwhile comment 
about the diagnostic value within the family of 
microscopic structures, except that anatomy is 
relatively uniform throughout the Pandanaceae 
and emphasizes its naturalness. In the survey a 
considerable range in stomatal structure was 
found, especially in Pandanus, a range not fully 
described by previous observers like Kofler 
(1918), Sofia (1884), or Solereder and Meyer 
(1933). Observations were extended to indicate 
the range of stomatal structure throughout a 
single plant, whereupon it was discovered that, 
in certain instances, the full range of stomatal 
variation within the genus could be demon- 
strated within a single individual. This can be 
explained when the growth habit of Pandanus 
is understood. 
It was felt that a general summary of stomatal 
structure in Pandanaceae would be a signifi- 
cant contribution to the literature on monocot- 
yledonous anatomy. The present account deals 
1 Fairchild Tropical Garden, Miami 56, Florida. 
Manuscript received September 27, 1963. 
largely with Pandanus, notes on Freycinetia and 
Sararanga being included when they show out- 
standing features. Material of some 50 species 
has been examined during the course of this 
study, which — in view of the richness of Pan- 
danus, estimated at 500-600 species, and of 
Freycinetia, at 180-200 species (St. John, I960) 
— indicates how provisional this study is. It is 
not, therefore, intended as an exhaustive survey 
of the subject, but gives a clear indication of 
the known range of stomatal structure in Pan- 
danaceae and points the way to more intensive 
study. 
MATERIAL AND METHODS 
The survey is largely based on herbarium 
material of Pandanus supplied from specimens 
in the Bernice P. Bishop Museum, Honolulu, 
Hawaii, by Dr. B. C Stone, the material being 
selected to represent a wide range of subgenera. 
It was supplemented by material collected by 
myself and others in the wild, and by material 
in cultivation at the Fairchild Tropical Garden 
and the U. S. Department of Agriculture Experi- 
ment Station, Old Cutler Road, Miami, Florida. 
Slides and specimens in the collections of the 
Jodrell Laboratory, Royal Botanic Gardens, Kew, 
38 
