Author: J.E. Smith, 1793
Etymology
Named for 18th century Swiss botanist E. Davall.
Description
Roots restricted to the ventral side of lateral buds. Scales of rhizome peltate or basifixed with cordate base and greatly overlapping lobes, variously shaped: distinctly acicular, or flat and nearly acicular, narrowed evenly towards the apex, or narrowed abruptly from a broad base, or broad, ovate to oblong-subdeltoid with round to acute apex. Petioles usually well developed, in two ranks on the dorsal side of the rhizome; adaxial face sulcate, the groove usually raised in the middle; small species sometimes with subsessile leaves; petiole occasionally persistently scaly. Lamina simple, imparipinnate, pinnate + pinnatifid, bipinnate + bipinnatifid, or tripinnate + tripinnatifid; if compound deltoid and broadest towards base or rarely elongate, glabrous or rarely bearing multicellular hairs, anadromous or rarely isodromous or catadromous and then the scales evenly narrowed towards the apex; lamina dimorphic or monomorphic, in dimorphic species with reduced leaf tissue and/or more dissected. Vein endings on sterile segments reaching the margin or not. False veins present in several species. Rachis winged and therefore seemingly grooved adaxially but convex between the wings. In the dry state (re herbarium specimens) it is difficult to see whether the rachis itself is grooved or flat. Sori typically separate but in D. undulata connate and elongate along leaf margins; sori near the margin, facing midveins at the forking point of veins or at the bending point of a vein.
Spores (by Gisela Rödl-Linder). The spores are ellipsoidal with monolete aperture. The exospore is colliculate-verrucate, discretely verrucate, to fused verrucate to porous (the verrucae fused to the extent that the surface appears porous). All transitions occur between the different types, but generally the type is constant for a species or group of species.
In the former genus Araiostegia the perispore was described as granulate, contrary to the generally smooth perispore of Davallia . However, this character occurs only in one species, Davallia (Araiostegia) clarkei . The species of the former genus Araiostegia vary in the ornamentation of the exospore in the same way as the species of Davallia . Porous spores, which are rare in Davallia , do not occur in Araiostegia . Because closely related species generally possess the same kind of spores, I doubt whether the former genus Araiostegia is monophyletic.
In Davallia porous spores are found in Davallia heterophylla together with a transition of fused verrucate to porous, in Davallia seramensis , and in Davallia sessilifolia . In Davallia sessilifolioides , which is closely related to the latter, a transition of fused verrucate to porous spores is found. This type is also found in Davallia wagneriana and Davallia corniculata , two closely related species. In a few collections of the variable Davallia repens , that is here suspected to show introgression with the latter two species, the same type also is found. The size of the spores of Davallia repens varies between 27 and 46 µm, the spores of Davallia wagneriana and Davallia corniculata possess about the size of the smallest spores of Davallia repens . As there is one apogamous triploid reported, and the size varies throughout the area of distribution, I suppose that hybridizing resulting in triploidy and possibly polyploidy is the cause of the extreme high variability in Davallia repens . The rest of the collections of Davallia repens studied possess fused verrucate spores, that are often transient to the fused verrucate to porous spores. Moreover this type of spore is found in Davallia heterophylla and Davallia undulata , species that are quite different. Davallia parvula , a species very near to Davallia repens , has rugate-verrucate spores that show a bit more fusion of the verrucae but closely resembles the spores of Davallia repens ; they fall within the variability of Davallia repens in size and ornamentation. This type is also found in the distinct Davallia pectinata . Many species possess colliculate-verrucate spores, that are rather constant for a species although transitions may be found within one collection with discrete verrucate and discrete to fused verrucate. There is in this large group no correlation with other characters. Davallia canariensis differs from all the other species in the verrucae being distinctly tuberculate.
Chromosomes
In Davallia x = 40, in Davallia repens from Sri Lanka triploidy and apogamy is reported (Manton and Sledge, 1954).
Distribution
From India through continental Southeast Asia to China, Korea, and Japan; Malesia; the Pacific to Samoa and New Zealand; NE. Australia; the islands in the Indian Ocean; Africa; one species in NW. Africa, the Canary Is., and SW. Europe.
Eight species are restricted to a very small area: Davallia assamica to Assam and neighbouring areas, Davallia brassii to a small area around the border of Irian Jaya and Papua New Guinea, Davallia leptocarpa to Aneityum in the New Hebrides (Vanuatu), Davallia rouffaeriensis to a very restricted area near the Rouffaer River in Irian Jaya, Davallia sessilifolioides to Seram, Davallia speciosa to Moulmein in Burma, Davallia tasmani to Three Kings island, north of New Zealand, and Davallia undulata to Halmaheira and Ternate in the Moluccas.
Two species have a very wide distribution, Davallia denticulata from tropical West Africa to the Society Islands in the Pacific and Davallia repens from tropical West Africa to Samoa. The latter species is found as far north as Japan and as far south as the Kerguelen (The large variability is discussed under this species. Whereas in the outer ranges of its distribution the species is rather constant, it is highly variable in the inner regions where it comes into contact with other species of the genus). The majority of the species have a moderately large area of distribution in Southeast Asia, 11 genera extending far into the Pacific: Davallia brevipes, Davallia denticulata, Davallia embolostegia, Davallia falcinella, Davallia heterophylla, Davallia pectinata, Davallia sessilifolia , Davallia solida , and Davallia pentaphylla .
Davallia leptocarpa and Davallia graeffei are restricted to the Pacific.
The distribution of Davallia canariensis , in northern Africa and southwestern Europe, lies outside the area of the rest of the genus just as the distribution of Davallia tasmani at the other side of the globe. Nevertheless both species are so similar that they could be varieties (Map1; Map2; Map3, species of Davallia ).
The recent centre of distribution of the genus (and of the family) is clearly Malesia with 23 of the total 34 species and 9 endemic species. Malesia and the Pacific together possess 16 endemic species. The island of Sumatra contains 16 species, Borneo 14, the Philippines 13, the Moluccas 15, New Guinea 14, but the Pacific also has a large number of species, viz. 14, of which three (one in New Zealand) are endemic. The species endemic to Asia north of the Isthmus of Kra in Southern Thailand number only 7 (Map4).
The distribution of so many taxa far into the Pacific may be explained because the adverse trade and monsoon winds usually do not blow during the time there are spores. Then the winds blow towards the Pacific, at least in the Philippines. Davallia canariensis might be a relict from the Eocene epoch, but for the distribution of Davallia tasmani an explanation is difficult to find.