A Taxonomic Study of Juncus in Illinois

Abstract

A key and descriptions of the twenty-two species of Juncus occurring in Illinois is presented, with distribution notes and discussions of variation within the species. Juncus articulatus L. is shown to be absent from Illinois; Juncus gerardi Loisel. is newly recorded for the state. MORPHOLOGY The genus Juncus in Illinois is composed of glabrous herbs which are cespitose or rhizomatous perennials (except the annual J. bufonius). The stems vary from one centimeter to one and one-half meters in height below the inflorescence. Most of the species have leaves composed of open sheaths which bear linear or lance-linear blades. With the exception of J. bufonius, the species with blades have scarious or rigid auricles which may extend to five millimeters beyond the region where sheaths end and the blades are produced. Two species, J. effusus and J. balticus, have bladeless mucronate sheaths. The blades may be flat, involute, or terete. Except for the leaves of J. greenei and J. vaseyi, all the teretebladed leaves are hollow and provided with septa or cross-partitions at various intervals throughout their lengths. The inflorescences are paniculate or cymose, usually branched, and may be from contracted to greatly elongated and up to nearly three decimeters long. One or several unequal leaves or bracts originate below the inflorescences and may be shorter than to exceeding the inflorescences by nearly five decimeters. These are the involucral leaves. The inflorescences terminate the stems. In most species this is apparent. However, in J. balticus and J. effusus, the single involucral leaves are long and simulate the stems beneath, giving the inflorescences the appearance of being lateral on the stems. Thus, the only truly developed leaves in these two species are the involucral leaves, since the basal sheaths are bladeless. Adamson (1925) has discussed this condition. The flowers are mostly anemophilous, although cleistogamy has been observed in J. bufonius. The flowers are borne in either of two distinct ways: singly on the inflorescence branches or in groups of two to nearly ninety flowers in tight clusters known as heads. The flowers reach a length of seven millimeters. They have a three-celled or incompletely three-celled superior ovary which develops into a capsule. Various small bracts are present in the inflorescences. Also, in the species which do not have the flowers grouped in heads, there are present immediately below the perianths two small, paired bractlets known as prophylls. Bractlets subtending the prophylls often partly overlap the prophylls. The perianth is composed of six similar segments in two whorls. The three sepals and three petals are scarious-margined, ovate to lanceolate, obtuse to subulate, and green or brown in color. Most species regularly have either three or six stamens per flower. Two