Section V.
In this section are included those genera where within the same genus some inland species have been derived from the coast species whilst others have been originally brought by birds. Guettarda alone belongs here. In this genus we find, as is so frequently the case, a littoral tree (G. speciosa) widely spread in the Old World and ranging over the whole tropical Pacific as far east as Pitcairn and Elizabeth islands, but absent from Hawaii. Here also as with Pandanus it is only in the Western Pacific that we find inland endemic species so distinct in character from the littoral tree that they may be regarded as of independent origin.
Since, however, there is an inland form of the coast species in Tahiti (Guettarda speciosa, var. tahitensis) which, according to Drake del Castillo, is distinguished only by its more rounded leaves and by the more marked pubescence of the under leaf-surfaces, we evidently have there an inland species in process of development from the littoral species. This inland tree is found at elevations as great as 600 metres or almost 2,000 feet above the sea; and indeed if we follow Nadeaud the specific differentiation is complete. However, there is no doubt raised as to its close affinity to the beach tree; and we are almost compelled for another reason to regard it as a derivative of the shore species, because, as pointed out in [Chapter XXVII.], there are very few inland plants in the Tahitian flora possessing fruits as large as those of Guettarda that owe their presence in those islands to frugivorous birds.
Of the two inland species of the genus found in Fiji, G. inconspicua and G. vitiensis, it may at once be said that, as indicated in Dr. Seemann’s work, their characters are far from suggesting any connection in origin with G. speciosa, the shore-species, the inland and littoral plants belonging to different sections of the genus. In their case we can only look to the frugivorous bird for the explanation of their existence in the group. The fruits would be probably small; and in this connection it is to be noted that Mr. H. N. Ridley in his paper on the flora of Fernando Noronha evidently looks to birds to account for the presence of a species of Guettarda on the island, a species not found elsewhere.
But another inland Fijian form of Guettarda found by me in Vanua Levu at elevations of 1,000 to 1,400 feet above the sea, and dubbed by the natives with the name of the littoral tree (Mbua-mbua), corresponds in its close relation to G. speciosa with the inland Tahitian form of that tree, and is to all appearance a derivative of it. It is chiefly distinguished by its thinner, more hairy leaves, which taper at each end and are not subcordate at the base as is often the case with the leaves of G. speciosa. The coverings of the fruit are less fibrous and the putamen is not so deeply notched or grooved. The difference also extends to the buoyancy of the fruits in accordance with the principle laid down in [Chapter II.] Whilst those of G. speciosa float for many months and are of common occurrence amongst the stranded drift of tropical beaches, as for instance in the Keeling Islands, in the Solomon Group, and in Fiji, those of the inland species float only for a few weeks, their softer coverings decaying more rapidly in sea-water.
We seem therefore to have had two principles at work in Fiji in determining the origin of the inland species of Guettarda. Whilst in one case the inland species is so sharply distinguished from the coast species as to require the independent agency of frugivorous birds to explain its presence, in the other the inland form, as in the instance also of the Tahitian variety, is so much akin to it that the probability of derivation from it is very great.