A remarkable feature of the distribution of grasses is its uniformity; there are no great centres for the order, as in Compositae, where a marked preponderance of endemic species exists; and the genera, except some of the smallest or monotypic ones, have usually a wide distribution.
The tribe is very poorly represented in tropical Africa; one species Oxytenanthera abyssinica has a wide range, and three monotypic genera are endemic in western tropical Africa.
Pyrenaica, on a single high station in the central Pyrenees, and that of the monotypic genus Xatardia, only on a high alpine pass between the Val d'Eynes and Catalonia.
The monotypic Pringlea antiscorbutica, the Kerguelen Island cabbage, has no near ally in the southern hemisphere, but is closely related to the northern Cochlearia.
In the monotypic genus Bowenia the large fronds, borne singly on the short and thick stem, are bi-pinnate (fig.
Thus of the 90 indigenous genera (many monotypic or very small) only 14 are endemic, i extends to South Africa, 3 are common to Australia and New Zealand, 18 extend also into Asia, whilst no fewer than 54 are found in both the Old and New Worlds, 26 being chiefly tropical and 28 chiefly extra-tropical.
The number of endemic species is exceptionally large, the number of monotypic genera in the Peninsula greater than in any other part of the Mediterranean domain.
The numerous species of fronds from Jurassic and Wealden rocks of North America and Europe referred to Thyrsopteris, a recent monotypic genus confined to Juan Fernandez, are in the majority of cases founded on sterile leaves, and of little or no botanical value.
Wettinia occurs in Peru, Trithrinax in Chile with the monotypic Jubaea, Juania, also monotypic, is confined to Juan Fernandez.
An extinct water-lily, Euryale limburgensis, belongs to a monotypic genus now confined to Assam and China; an extinct sedge, Dulichium vespiforme, belongs to a genus only living in America, though the only living species once flourished also in Denmark; an extinct species of water-aloe (Stratiotes elegans) makes a third genus, represented only by a single living species, which was evidently better represented in Pliocene times.