Evolution in the Proteaceae.

Abstract

The sources of evidence bearing on the evolution of the Proteaceae are outlined. New cytological data are presented for Embothrium (South American), Beauprea (New Caledonian), and 15 Australian genera which are mostly tropical or subtropical and with morphological characters considered primitive. Beauprea, Buckinghamia, Opisthiolepis, Embothrium, Oreocallis, and Strangea have 2n = 22 and this number is also confirmed for Stenocarpus and Lomatia. Hollandaea, Darlingia, Cardwellia, Carnarvonia, Helicia, Hicksbeachia, Gevuina, Musgravea, and Austromuellera have 2n = 28. In all these cases the chromosomes are comparable in size with those previously described in Grevillea and other genera. Placospermum has 2n = 14 and its chromosomes are many times larger, comparable with those which have been reported in Persoonia.

The palaeobotanical evidence is discussed, but does not throw much light on the detailed phylogeny or on the origin of the family, although it suggests that Proteaceae were well developed in the Upper Cretaceous period. From comparative morphology and cytology, together with considerations of distribution, ecology, and other factors, the characters of the ancestral "Proto-Proteaceae" are postulated and an evolutionary scheme of probable relationships of subfamilies, tribes, and genera is put forward, but formal taxonomic rearrangement is deferred for a later publication. Morphological features of the ovule and seed and of floral orientation are discussed. The characters and probable evolutionary trends within each individual group are dealt with in detail and form the basis of a number of proposed rearrangements in the taxonomic system.

Placospermum is considered to combine many primitive morphological and cytological features, and it is excluded from both the subfamilies Proteoideae and Grevilleoideae, being thought to represent an early offshoot before the differentiation of those groups. The Proteoideae are probably polyphyletic but the Grevilleoideae represent a more close-knit assemblage.

Within the subfamilies certain groups consist of clearly allied genera and appear to be monophyletic. These constitute the majority of the formally recognized tribes, viz. Proteeae (here including Synaphea and Conospermum), Grevilleeae (here restricted to Finschia, Grevillea, and Hakea), Musgraveeae (Musgravea, Austromuellera), and Banksieae. The tribe Embothrieae, here restricted to those genera of the Grevilleoideae with n = 11, shows considerable morphological diversity but is accepted for the present. It is shown that Strangea should be removed from the Grevilleeae and placed in the Embothrieae near Stenocarpus, with which it shares distinctive seed and inflorescence characters.

Some isolated genera, viz. Orites (Grevilleoideae) and in particular Franklandia (Proteoideae), show marked specialization in many features and may be given tribal status. The other two tribes recognized, Persoonieae (in the Proteoideae) and Macadamieae (in the Grevilleoideae), consist of genera which, although advanced in certain respects, preserve numerous primitive features. Each of these tribes comprises a number of groups and individual genera which appear to be the result of evolutionary lines that have been independent from a very early stage. The African genus Brabeium, formerly placed in Persoonieae, is shown to be related to Macadamia.

There remain certain genera, viz. Dilobeia (Proteoideae) and also Hollandaea, Knightia, Darlingia, Cardwellia, and Carnarvonia (Grevilleoideae), for which no formal grouping is at present suggested.

The frequent independence of trends of specialization in individual characters is stressed, and the relationship of zygomorphy and other floral and inflorescence specializations to pollination by higher insects and birds is discussed. The primitive condition of the inflorescence is considered to have been essentially racemose, not a thyrse as recently suggested. Racemose inflorescences are found in many Proteoideae but the apparent raceme in Grevilleoideae is thought to be a reduced panicle.

The phytogeography of the family is briefly discussed. There is evidence indicating a tropical origin, and therefore suggestions of southern connections between Australia and Africa are discounted, though they may have occurred between Australia and South America.

Stress is placed on the need for an understanding of evolution within the family as a prerequisite to the development of theories on its position among the Angiosperms and on its historical phytogeography.