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Guides Corner These notes graciously provided by Jason Dewees from his presentation. Jason is a writer who is active in the International Palm Society and California Horticultural Society and volunteers at the Conservatory of Flowers and the San Francisco Botanical Garden. He is a partner in Palm Sundae, palm specialists. www.palmSundae.com Arecaceae: The Palm Family What are palms? Palms are flowering plants - monocots, like orchids, grasses, agaves, amaryllis, gingers and other plants that have single seed-leaves, flower parts in multiples of three, and parallel leaf veins and adventitious roots . Their diversity of form is greater than any other monocotyledonous family. The earliest palm fossil is 80 million years old.
Amazing palms The family boasts many plant-kingdom extremes:
How do you identify a palm? Look at their leaves and stems. The leaves develop from a single bud atop each stem, unfolding like an accordion or a fan. Leaf bases encircle the stem, at least early in their development. The stems of mature (flowering-age) palms are tough and woody, even if buried in the soil like a rhizome. The plants most difficult to distinguish from palms, owing to their similarly folded leaves, are members of the family Cyclanthaceae, such as the "Panama Hat Palm," Cardulovica palmata, but their stems are not woody. Curculigo spp., in the family Hypoxidaceae, resemble palms too, but also lack woody stems. Palm forms The palm leaf consists of a petiole (leaf stem) and blade (the main "body" of the leaf). Leaves fall into two main categories, palmate and pinnate-fan-shaped and feather-shaped. Think of the common Mexican or California Fan palm, Washingtonia, for an example of the palmate type and the coconut and date palms for the feather type. In most pinnate palms, the blade is divided into leaflets; they attach to the rachis, an extension of the petiole through the blade. Within these two leaf forms are a few variations: Some palmate species' leaves have a costa that extends from the petiole into the blade, with the effect of slightly (or strongly) folding the fan into two halves; this leaf form is costapalmate. Some pinnate (feather) leaves have secondary rachises off which spring the leaflets; this leaf form is bipinnate, and it's mostly found in Caryota, the fishtail palms. Some species of both palmate and pinnate palms have undivided leaves, with no divisions between the accordion-like segments of the blade. (These are particularly beautiful ornamentals.) Some have blades with irregularly divided segments. Where the leaf meets the trunk in some pinnate species, you may find a crownshaft, a green or pigmented sheath encircling the trunk and cleanly dropping from the stem to reveal the next-higher leaf. Think of Cyrtostachys renda, the Sealing-Wax Palm. Most species, however, have sheaths that split or disintegrate by the time the outermost/lowest leaf is visible. Of these, some drop cleanly from the stem when dead, and many cling for months or years. Petioles may be smooth and unarmed or thorny. If you like thorns and needles, you can find a species of palm with armament on any organ, from inflorescence to stem and from blade to root. Chemical weapons (calcium oxalate crystals) have been found in fruits of the genus Caryota, and puncture wounds of Phoenix canariensis, the Canary Island Date palm flanking the Conservatory entrance, will almost invariably leave persistent painful infections. Palm habits They grow mostly as single-stem trees, but some palms develop multiple stems from a single root system, like bamboo; some are vines or shrubs with buried or sprawling trunks. Because each stem has but one growth point, if you, PG&E tree crew, kill that bud up there, you kill that stem. Stem thicknesses range from pencil to more than a meter. Aboveground branching is rare except in the genus Hyphaene. There are no true epiphytes in the family, but at least one, Ravenea musicalis, is a true aquatic, and a few tolerate extended drought, like Ravenea xerophila and Medemia argun. Most desert palms grow near perennial water sources, however. Some species tolerate sun from a young age, but most, being from forest habitats, prefer shade as juveniles, and understory species insist on lifelong shade. Most species bloom and fruit throughout maturity, with inflorescences of some emerging from among the leaves, while those of others emerge below the lowest leaves. Some species are monocarpic: They grow through a vegetative phase and then bloom, fruit and die. One monocarpic genus of massive costapalmate palms, Corypha, develops an apical inflorescence, the largest in the plant kingdom, as an endgame. In fruit, it looks a bit like a giant Christmas tree with an oversized brown skirt draped atop an enormous post. Palms are integral to tropical rainforest and seasonal forest habitats. They also extend into montane, cloud forest and savanna habitats, with outliers in warm deserts, subtropical and temperate forests, and even mediterranean-climate habitats. A renowned specimen of the rare Chilean Wine palm, Jubaea chilensis, native to the central Chilean matorral, grows across John F. Kennedy Drive from Fuchsia Dell Drive. The species is known for having the thickest trunk of all palms. See palms outdoors: Oakland Palmetum at Lakeside Garden Center across from Children's Fairyland in Lakeside Park, Oakland; SF Botanical Garden at Strybing Arboretum; UC Berkeley Botanical Garden; Huntington Botanical Gardens, Pasadena; LA County Arboretum, Arcadia, & Virginia Robinson Botanical Garden, Beverly Hills; Quail Gardens, San Diego Zoo & Balboa Park, San Diego County; Palm (Indian) Canyon, Palm Springs; Anza-Borrego State Park; Honolulu Botanical Gardens (esp. Ho'omaluhia, Foster, Wahiawa & Koko Crater), Lyon Arboretum & Waimea Valley Audubon Center, O'ahu; National Tropical Botanical Gardens (Allerton & McBryde), Kaua'i; Fairchild Tropical Garden, The Kampong, & Montgomery Botanical Center, Miami; Rio de Janeiro Botanical Garden; Singapore Botanical Garden; Nong Nooch Botanical Gardens, Thailand; Palmetum of Santa Cruz de Tenerife, Spain. |
