I’ve just finished reading On the Vegetation of the Galapagos Archipelago, as compared with that of some other Tropical Islands and of the Continent of America by Sir Joseph Dalton Hooker, who was born 194 years ago today.
In 1844, Darwin asked Hooker to work up his botanical samples from the Galapagos and thus began their life-long friendship. In working them up, Hooker included specimens collected by others, although Darwin’s collection was by far the largest. He read his findings to the Linnean Society in 1846 and the paper was published in 1851.
In this study, you can see how Hooker gravitated toward establishing biogeography as a science. He noted that all flora from any country can be separated into two classes: indigenous and introduced. In the Galapagos, the introduced species were most closely related to plants in the West Indies and Panama whereas the indigenous species were most closely related to mountainous and other “extra-tropical” parts of the Americas.
But the part of the work that most caught my eye was his description of the Compositae (now Asteraceae).
The Compositae are in every respect the most remarkable family in the Galapagos, both as regards number of new species and new genera, and from their forming much of the wood of the islands.
“Their forming most of the wood of the islands.” – I have been astonished to find Asteraceae trees here in Panama, and now I learn that they accounted, in Darwin’s time anyway, for most of the wood in the Galapagos!
They also are the most instructive, as the species are very clearly defined: the peculiar genera have representatives in the different islets; and whilst the new species are almost wholly allied to plants from the Andes or extra-tropical parts of America, the old are almost universally the weeds of the low coast of the same continent.
Just the opposite of other families! As noted above, in the other families the introduced species were most closely related to plants in the West Indies whereas the indigenous species were most closely related to continental parts of the Americas. He attributes this distinction to the methods of dispersal – that the seeds of the Compositae are wind-blown whereas many of the other seeds can be carried on ocean currents.
Hooker was a highly respected botanist and, like his father, became director of the Royal Botanic Gardens at Kew. We’ll probably be seeing more mention of him toward the end of the year, when the
200th 100th anniversary of his death will be marked on December 10.