Vegetative Reproduction Observed in Ophioglossum pusillum Raf.

Abstract

A Massachusetts population of Ophioglossum pusillum was studied to examine root connections between fronds. A 0.5 m2 sample section of turf contained 38 fronds, including a network of 10 fronds connected by a single root system approximately 40 cm long. Apparently large colonies of this species may consist of few genetically distinct elements, which may help to explain the lack of genetic variability found in some populations. The branching of the rhizome and formation of adventitious buds on roots in ferns of the Ophioglossaceae have been reported often (Petry, 1915; War- dlaw, 1953; Bold, 1967; Peterson, 1970; Bierhorst, 1971; Foster and Gifford, 1974; Kato et al., 1988). Field observations include descriptions of a colony of seven sporophytes of Ophioglossum petiolatum Hook. with a common root system (St. John, 1949) and several colonies of 0. vulgatum L. (as 0. pycnos- tichum (Fernald) A. Love & D. Love) of from four to ten plants connected by common root systems (Cascio and Thomas, 1993). Similar reports have been published documenting vegetative reproduction in 0. pusillum Raf., the north- ern adder's-tongue fern, in the field. Most are of two sporophytes derived from a single root system. In a large New Hampshire colony, Blake (1913) observed the occurrence of two plants from a common rootstock and referred to her- barium specimens with similar arrangements. Hagenah (1966) reported that many plants in an interdunal meadow along Lake Michigan had two fronds originating from a single rootstock. Edwards (1982) traced a single root con- necting two fronds of 0. pusillum for 1.8 m in a pasture in southern England. In a 1991 survey of a population of 0. pusillum in Franklin County, MA, I counted 901 fronds in an area of approximately 1 hectare (McMaster, 1994). Clusters of from 10-27 fronds were frequently observed within a radius of 0.5 meters. During summer, 1994, I excavated a 0.5 m2 section of turf from this wetland containing approximately 38 fronds of 0. pusillum. By carefully re- moving soil and dead vegetation and untangling the root systems of other vascular plants, I attempted to isolate the root system of each 0. pusillum. One cluster of ten fronds (seven with fertile fronds) of 0. pusillum was found to be connected by a dense network of roots (Fig. 1). The network was approximately 40 cm in overall length. It included one rhizome bearing two fronds, eight rhizomes bearing a single frond each, and three rhizomes with no frond. The largest rhizome had 26 lateral roots; another had 24. The small- est rhizome had six lateral roots. Several lateral roots appeared to have been severed during excavation. Root connections were found for six other clusters, each with from two to ten fronds, and each with severed roots. These observations suggest that apparently large colonies of 0. pusillum may