For some time I have been carefully rechecking determinations of ferns and tree ferns at MEMBG. For many tree ferns, the scales along the petiole bases are very useful for identification. Gordon DeWolf was the first to use scales for classification in 1953, identifying paleotropical species of the family Cyatheaceae. Later, Richard E. Holttum used scales for taxonomic treatments of Cyathea. Rolla Tryon from the Gray Herbarium at Harvard published a helpful classification of Cyatheaceae in which he split Cyathea into several genera based on morphology of petiole scales. Barbara Joe Hoshizaki, for decades the UCLA fern curator, followed Tryon's treatment of Cyatheaceae in her popular Fern Growers Manual (1979). Nevertheless, many botanists and horticulturists do not recognize the segregate genera and continue to use only Cyathea. Whether one accepts Tryon's treatment or not, the scales provide a useful taxonomic character.
In late February, while sliding my hand along the petiole of an Australian tree fern, Cyathea cooperi, to collect scales, some of the scales became airborne, and at least one landed in my right eye. The pain and irritation were intense, and after several futile attempts to remove the scale on my own, I sought professional help at the Occupational Health Clinic on campus. After numbing the eye to examine it, clinical staff found the cornea was scratched, but they could find no scales or foreign objects on the eyeball or embedded on the inside of the eyelids. I was given painkillers and released, but even before I had returned to my office the numbing medication had worn off, and intense pain returned. I was convinced that a scale was still in my eye. After three more clinic visits, higher magnification revealed a small scale that was finally removed. Only then did pain and irritation cease, I recovered rapidly. At the time of this writing, visual acuity--hopeless in my myopic condition--has not yet returned to pre-injury state, but should it return when the corneal epithelium heals completely and becomes smooth.
Was my mishap unique? I contacted Barbara Joe Hoshizaki to ask if she knew of a similar case and found that I am not alone--she had also been a victim! Kei Nakai, a UCLA alum and garden supporter, informed me that during hot, dry weather scales are particularly apt to become dislodged when potted plants are moved or fronds pruned, and can cause severe itching. David Verity, retired MEMBG senior museum scientist, also suffered severe itching when he transplanted C. cooperi. So all of us in this "club" of tree fern victims advise anyone working with this species to wear eye protection during any activity, such as pruning, that would result in making scales airborne.
Although so far I have found no mention in the literature about the function of these irritating fern scales, they undoubtedly have an ecological function, probably to deter herbivory. It is easy to imagine that the scales illustrated below could be very irritating to the mouth and throat of an herbivore. Scales are denser and larger at the bases of the petioles, possibly helping to shield the apical meristem, but small scales are distributed all over the underside of the frond of C. cooperi.
Species in other families lack scales but have uniseriate, multicellular hairs, which are short and coarse in Dicksonia (Dicksoniaceae) and long and very fine in Cibotium (Thelypteridaceae).
As for the tree ferns in our garden, they put up a good fight, but I feel that I have won. While some have not yet achieved tree-like size, all are properly named and labeled.
When you visit the fern section, I hope that you will be pleased with the signage.
BARRY PRIGGE (Senior Research Associate)