The Development of Plantlets from Strobilus Branches in Lycopodium phlegmaria

Abstract

Lycopodium phlegmaria L. is an epiphyte commonly found growing on the trunks and branches of forest trees in Singapore. It is a widely distributed species in the Old World tropics, ranging from Africa to Polynesia. Its pendulous stems are covered with spirally arranged, stiff, ovate-lanceolate leaves (Fig. 1). Both the sterile portions of the stems and the strobili branch dichotomously (Figs. I and 2). The sporophylls are smaller than the foliage leaves and are arranged more compactly along the branches. In most cases, the sporophylls are grouped terminally on determinate stems. However, instances of foliage leaves appearing along the strobilus branches have been observed (Fig. 2). This is reminiscent of the condition seen in L. selago L., where the fertile zones alternate with the sterile and the foliage leaves are not much different from the sporophylls (Bower, 1935, p. 200). Recently, a portion of L. phlegmaria detached from the parent plant was found lying on damp ground on the secondary forest at the MacRitchie Catchment area in Singapore. It was still green, and the ends of the fertile branches showed growth following detachment. Under the humid conditions of the forest floor, the ends of the branches had reverted to vegetative growth and had produced one or two young plants each (Fig. 4). Roots had grown from the base of some of these young plants. In one instance, the extension of a strobilus branch was an elongate stem with long internodes (Fig. 3). At the nodes were leafy structures similar to the sporophylls. In the axils of these structures were obviously vegetative buds, some of which had developed into vegetative shoots (Fig. 3). Longitudinal sections of the strobilus branches revealed the gradual transformation of the sporangia from fertile to sterile in the acropetal direction. The fertile, spore-containing sporangia had thickened outer cells along the inner and radial walls. Sterile sporangia lacked these characteristically thickened outer cells. Sporangia along the vegetative outgrowths were mere protuberances, without any differentiation whatsoever. As in ferns, root development was endogenous and very close to the vascular strand. Placing the ends of strobilus branches from cultivated L. phlegmaria on moist vermiculite similarly stimulated development of vegetative shoots after about four months. The new growths had excessively elongate interodes, the sporophylls were smaller until foliage leaves were produced when the axis turned upwards. Roots formed at the points of turning after a further period of two to four months. These shoots could then be removed as plantlets. These observations give support to Bower's (1908, p. 164) theory that foliage leaves essentially are sporophylls with the sporangia completely suppressed. In this respect, it should be noted that the strobili of L. obscurum L. and L. flabel-