The Island of the Colorblind

Cycads had huge seeds, so strongly constructed and so packed with nourishment that they had a very good chance of surviving and germinating. And they could call on not just one but a variety of vectors for their dispersal. All sorts of smaller animals – from bats to birds to marsupials to rodents – attracted by the brightly colored, nutritious outer coat, would carry them off, nibble at them, and then discard the seed proper, the essential inner core, unharmed. Some rodents would squirrel them away, bury them – in effect, plant them – increasing their chances of successful germination. Large mammals might eat the entire seed – monkeys eating individual seeds, elephants entire cones – and void the endosperm, in its tough nut, unharmed in their dung, often in quite far-removed places.

Beata was examining another cycad plant, speaking softly in Chamorro to her son. When the rains come, she was saying, the seeds can float. You can tell where they float to in the jungle, because new cycad plants sprout up all along the little rivers and streams. She thinks they float in the sea as well, and that this is how they get to other islands. As she spoke she split open a seed, and showed me the spongy flotation layer just beneath the seed coat – a feature peculiar to the Marianas cycad and the other littoral species of Cycas, which grow in coastal and near-coastal forests.

Cycads have spread to many different ecoclimes, from the humid tropical zones they flourished in during the Jurassic, to near-deserts, savannahs, mountains, and seashores. It is the littoral species which have achieved the widest distribution, for their seeds can float and travel great distances on ocean currents. One of these species, Cycas thouarsii, has spread from the east coast of Africa to Madagascar, to the Comoros and the Seychelles. The other littoral species, C. circinalis and C. rumphii, seem to have originated in the coastal plains of India and Southeast Asia. From here their seeds, borne on ocean currents, have fanned out across the Pacific, colonizing New Guinea, the Moluccas, Fiji, the Solomon Islands, Palau, Yap, some of the Carolines and Marshalls – and, of course, Guam and Rota. And as the buoyant seeds of the ancestral species have settled on different islands, they have begotten striking variants, some of which have diverged now, in a manner which would have delighted Darwin, to half a dozen new species or more.[91]

Although cycads vary greatly in size and character, from sixty-foot trees to delicate plants with underground rhizomes, many of the sixty-odd species of Cycas do not look that different (as opposed, say, to the species of Zamia, which vary so widely, and wildly, in appearance that one has difficulty believing they all belong to the same genus) – and that one of these species should be mistaken for another is very understandable. Indeed, I had been surprised, after my Guam visit, when I went into a nursery in San Francisco, thinking to buy a Cycas circinalis for a wedding present – and was shown a plant which was clearly different from the Guam one. When I queried the nursery owner, she indignantly insisted that it was a circinalis, and suggested that perhaps what I had seen in Guam was not. It seemed astonishing that there should be such confusion even among plant experts – but David Jones, in his Cycads of the World, speaks of the complexities of identifying the island cycads:

The plants adapt over generations in various small ways to their own particular environmental circumstances and local climate.…The situation is further complicated by new arrivals being regularly carried on ocean currents. On reaching maturity these recent plants can hybridize with existing plants and the resulting complex range of variation may defy taxonomic separation. Thus C. circinalis must be regarded as an extremely variable species.

And indeed, since I returned from Guam, I have learned that the cycad peculiar to Guam and Rota, regarded for centuries as a variety of C. circinalis, has recently been reclassified as a distinct species within the C. rumphii ‘complex,’ and renamed C. micronesica.[92]