Studies in Phylogeny. II. On the Phylogeny of the Malaysian Burseraceae-Canarieae in general and of Haplolobus in particular

The Burseraceae comprise 3 tribes which show an increasing differentiation from West to East and have, accordingly, their points of gravity in America ( Protieae), Africa (Bursereae) and Asia to Australia-Polynesia (Canarieae) respectively. An eastward migration of the order is probable. The easternmost tribe comprises 5 genera, viz. Scutinanthe, Canarium, Santiria, Dacryodes and Haplolobus. These are tested regarding their fundamental characters, in order to calculate their ”phase indices“. In these calculations 1 (of the series 1, 1½, 2, 2½, 3) means the most primitive, 3 the most advanced condition of a feature. From the figures thus obtained and from geographical data, it is concluded that Haplolobus (area: Borneo to New Guinea inclusive; map 1) is the youngest genus of the five, whilst the four others must have originated in East Asia more or less simultaneously from the ”Procanarieae“ which where at that time still closely related to the ancestors of Garuga (Protieae). It is further evidenced both by the characters and by area disjunction that Haplolobus must have originated bi- or polytopically from Santiria in Eastern Malaysia. Santiria shows a recent species explosion in the Sunda Land, Haplolobus in New Guinea (map 2). In ”Wallacea“ the last-named genera are apparently either in regression (Santiria) or scantily developing (Haplolobus). The paper proceeds with considerations on migration tracks in Malaysia and adjacent regions (map 3), checked by a short survey of the geological history since the early Tertiary. From the last-named survey it is concluded that three different areas are in the way of genorheithra, migrating either eastward or westward in Malaysia, viz. 1. the old and large continental Sunda Land which enabled rapid migrations and large ”species explosions“; 2. ”Wallacea“ which with its continuous insular character has always been a serious impediment to migrations and which consequently is to be considered as a sieve for potentialities; and 3. the Sahul Land which is also continental, but younger and smaller than the Sunda Land. These conditions (among others) are responsible for the fact that so much more Asiatic types have reached Australia and Polynesia than Australian types reached Asia. The paper closes with a tentative reconstruction of the tertiary and quaternary phylogeny of the Canarieae in the region under discussion (fig. 1).