Branch and Inflorescence Production in Saw Palmetto (Serenoa repens)

Fisher, J.; Tomlinson, P.

The saw palmetto, Serenoa repens (Bartr.) Small (subfamily Coryphoideae) is widely distributed throughout the southeastern United States. It is common in pinelands, prairies and coastal sand dunes, typically with a lowgrowing habit. Most plants have extended underground or surface-creeping stems (Fig. ll) but sometimes it forms dense clumps. Occasional plants in sheltered or otherwise favored habitats are found with more upright, obliquely-rising or even erect stems with basal branches. Saw palmetto then approaches the habit of a typical multiple-stemmed palm. Both saw palmetto and its associated pines are adapted to fires that are common during the dry season of winter and early spring. In an area that has been burned early in the year, Serenoa subsequently shows a conspicuous greening when the charred stems send up their first new leaves. Regrowth is rapid, the green of the new leaves being evident within a few days of the fire and by mid-summer, recovery of the foliage is complete. In some areas of the Everglades fires destroy hardwood hammocks, leaving only the saw palmettos at the perimeters; these form saw palmetto "rings" up to several hundred feet in diameter (Craighead, 1971: 130). Although Serenoa is so widespread and so abundant in pastures that it has been considered a weed, there is lack of information about its growth habit and especially of the vegetative branching whereby it seems to spread. Even a casual examination suggests that Serenoa represents an exception to the general method of branching in clustering palms, in which branches arise as suckers from buds at the base of the main axis, at or below ground level. Good examples of this typical habit are provided by the native paurotis palm (Acoelorraphe wrightii). Many species in the genera Bactris, Phoenix and Chamaedorea further represent this clustering habit (Tomlinson, 1961). In all of these palms the upright seedling stem at first produces vegetative branches as suckers which originate from buds in the axils of the lower leaves. As the seedling axis develops further there is a switch from vegetative to reproductive branching. Axillary buds may at first abort, but later ones in the axils of more distal leaves grow out as inflorescences. Consequently suckering is restricted to the basal part of a stem and by repetition of this process on daughter axes, a cluster of stems is built up. Abnormal individuals in a few species produce vegetative branches at higher levels as "aerial suckers" (Davis, 1969). In Chrysalidocarpus species some branching normally occurs above ground level by initiation of vegetative buds in extra-axillary positions (Fisher, 1973). The normal situation in multiple-stemmed palms, however, is a clear distinction between a vegetative phase (with suckers) and a reproductive phase (with inflorescences). The two phases are sharply circumscribed. In contrast to this, Serenoa clearly produces a sequence of inflorescences and vegetative branches (suckers) along its horizontal axis, without a clear morphological distinction between vegetative and flowering phases. In the following study we have examined some details of the relative frequency of vegetative and inflorescence buds in order to provide quantitative data.

Branch and Inflorescence Production in Saw Palmetto (Serenoa repens)

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