Non-axillary branching in the palms Eugeissona and Oncosperma (Arecaceae)

Abstract

Non-axillary branching in the palmsEwgeissona and Oncospermlr (Arecaceae). The south-east Asian palms, Eugeissona (Calamoideae) and Oncosperma (Arecoideae) are multiple-stemmed. The morphology and development of branching in two species of each genus were examined in Singapore, Borneo, and the Malay Peninsula. Cultivated seedling and adult plants of 0. tigzllarium were also observed in Florida.A new shoot arises most often from a longitudinal abaxial groove at the base of an enclosing leaf sheath. In some instances, especially in E . Irish, the enclosing leaf has two equal, adjacent grooves such that any distinction between an original mother shoot and a lateral daughter shoot is impossible. No axillary buds occur in Eugeissuna which is hapaxanthic. In Oncosperma, which is pleonanthic, axillary buds are absent from young pre-flowering stems, but an inflorescence bud occurs in the axil of each leaf in older aerial stems. Early ontogenetic stages of vegetative branching, as seen in sectioned apices, indicate that a new vegetative shoot is present on the abaxial base of the first (youngest) leaf primordium. There is no ontogenetic evidence for the displacement of an originally axillary meristem as previously described for the palm Salacca (Calamoideae). Shoot development in Eugeissona is interpreted as a putative dichotomy of the apical meristem in which the meristem centres commonly develop unequally. In Oncosperma the smaller sucker bud meristern may be described as an abaxial leaf base bud, but ontogenetic variations indicate this form of branching is close to dichotomous branching. These new examples of non-axillary branching are compared to similar cases previously reported for palms and other monocotyledons.

A 2300 yr record of sago and rice use from the southern Kelabit Highlands of Sarawak, Malaysian Borneo

“…BP representation of the sago palm tree Eugeissona appears much higher in comparison with most other plant species growing near the channel, with the exception of Cyperaceae, whilst charcoal flecks and pieces are present throughout this period. Eugeissona is hapaxanthic (Fisher et al, 1989) and under natural conditions it would be unlikely or indeed rare to find Eugeissona pollen grains amongst the pollen counts. These results therefore provide the earliest indication of sago management in the Kelabit Highlands.…”

Gynoecium and fruit histology and development in Eugeissona (Calamoideae: Arecaceae)

“…Nevertheless, the histogenesis of the pyrene in Eugeissona has not been described in the literature. Recent data support the isolated position of Eugeissona among Calamoideae, which is also supported by other morphological characters (Dransfield et al ., 2008); for example, the branching by putative dichotomy of the apical meristem (Fisher, Goh & Rao, 2008), partial centrifugal stamen development (Uhl & Dransfield, 1984) and by unique nectar with high concentrations of alcohol, securing pollination by small arboreal mammals (slow loris, pentailed tupaias, etc.) (Wiens et al ., 2008).…”