Flower Morphology and Plant Types Within <I>Juncus Roemerianus</I>

FLOWER MORPHOLOGY AND PLANT TYPES WITHIN JUNCUS ROEMERlANUS

LIONEL N. ELEUTERIUS Gulf Coast Research Laboratory Ocean Springs, Mississippi 39564

ABSTRACT Two plant forms were found to occur within funcus roemerianus, one consistently producing perfect flowers and the other producing pistillate flowers. Staminate flowers were not found. Pistillate flowers have aborted stamens. Rhizomes bearing inflorescences and transplants were dug out and used in the study. These observations serve to clarify previous inconsistent descriptions of floral morphology.

INTRODUCTION funcus roemerianus Scheele is a rhizomatous perennial which occurs in salt marsh from New Jersey to northern Florida on the Atlantic Coast and from south Florida to Texas along the Gulf Coast of the United States. In Mississippi, the species dominates approximately 96% (61,000 acres) of the coastal marsh and contributes significantly to estuarine productivity (Eleuterius 1972). During a recent autecological study of funcus roemerianus detailed investigations of flowers and corresponding plant types were included (Eleuterius, In preparation). It is apparent that some confusion exists in the literature regarding flower type and distribution within the species. Scheele (1849) first described and named f uncus roemerianus from plants bearing perfect flowers collected on Mustang Island at Galveston, Texas. Engelmann (1868) stated that he found "a rare form of J. roemerianus where both circles of stamens were suppressed or rather under- developed and in a rudimentary state so that those plants become unisexual." He also noted that J. roemerianus was the only species of Juncus in which occasionally unisexual specimens occur. Corresponding male plants were not seen, but he suggested that they may exist. The specimens that he observed were from Georgia and Florida. Chapman (1897), Small (1903, 1933), Buchenau (1906), Fernald (1950), Correll and Johnston (1972), all described the species as dioecious; Gleason (1952) and Radford, et at. (1968) as having perfect flowers, Long and Lakela (1972) as having unisexual flowers. Seibert (1969) reported that staminate, pistillate and perfect flowers of funcus roemerianus occurred on the coast of North Carolina. He also

Manuscript accepted September 10, 1973. 494 Bulletin of Marine Science [24(3)

FIGURE 1. Juncus roemerianus. Flower types drawn to scale. A. Perfect flower at anthesis (approximately 4.5 mm). B. Capsule resulting from perfect flower. C. Imperfect (pistillate) flower at anthesis. Note aborted stamens. D. Capsule resulting from imperfect flower. 1974] Eleuterius: Flower Morphology of funcus roemerianus 495

TABLE 1 COMPARATIVE MEASUREMENTS OF PERFECT AND PISTILLATE FLOWER PARTS OF JUNCUS ROEMER/ANUS (Data based upon 100 mature flowers randomly selected from 25 inflorescences representing the J. roemerianus population in salt marshes of Mississippi) ._~- Pistillate flowers Perfect flowers Range Average Range Average Flower Part (mm) (mm) (mm) (mm) Stigma length 2.0-3.0 2.5 1.0-2.0 1.5 Style length 1.0 1.0 0.2-0.7 0.5 Sepals length 2.5-3.2 3.0 3.7-4.2 4.0 Petals length 2.2-2.7 2.5 3.2-4.0 3.5 Carpel length 2.5-4.0 3.5 2.5-3.5 3.2 Flower length 4.5-6.5 5.5 3.5-6.0 4.5 Filament length rudimental 0.1-0.7 0.5 Anther length rudimental 1.5-2.5 2.0 Stamen length rudimental never over .5 -----"-- indicated that the various flower types occurred on the same plant and in the same inflorescence. This paper was prepared to clarify the description of floral morphology of funcus roemerianus and the distribution of flower types within the species.

METHODS AND MATERIALS

Specimens of funcus roemerianus were collected throughout the range of the species. Both herbarium and living specimens were obtained. Sev- eral hundred rhizomes bearing inflorescences were dug out during anthesis and studied. This was accomplished by washing the sods carefully to ob- tain rhizomes bearing two, three or four culms. Transplants of known flower type were placed in experimental areas. Comparative and develop- mental study of inflorescence and individual flowers were conducted.

RESUL TS AND DISCUSSION

Only perfect and pistillate flowers were found, although thousands of inflorescences representative of the entire funcus roemerianus dominated marsh of Mississippi were examined. Additional inflorescences representing smaller samples, collected from Texas, Louisiana, Alabama, Florida, Georgia, South Carolina and North Carolina also contained either all 496 Bulletin of Marine Science [24(3) perfect or all pistillate flowers. Extensive study of the rhizomes showed that during the period of anthesis they bore inflorescences composed entirely of pistillate or perfect flowers. Thus, a given rhizome produced only one flower type, but never both. Transplanted clonal material from bisexual and unisexual plants have for three years consistently produced only the respective flower type. Unisexual and bisexual colonies derived from single plants growing without competition on spoil areas have also consistently each produced only one flower type. These data indicate that there are two forms of funcus roemerianus; one which produces only bisexual flowers and one which produces only unisexual (pistillate) flowers. No staminate (unisexual) flowers have been found. This species is there- fore gynodioecious. Illustrations of the two flower types and respective mature capsules are shown in Figure 1. Comparative measurements of the bisexual and unisexual flower parts of funcus roemerianus are shown in Table 1, based upon mature flowers collected in the marshes of Mississippi. Flowers collected from other states fall into the ranges determined. Unisexual flowers have the longest stigmas and styles, whereas bisexual flowers have the longest sepals and petals. The longest carpels are found in unisexual flowers, the average difference in length being one (1) millimeter. The mature capsule of unisexual flowers is exserted as it extends to equal or exceed the length of the sepals. In bisexual flowers the sepals and petals always exceed the mature capsule. Staminodes occur in unisexual flowers attached to the base of sepals and petals, they are short and thick in immature flowers but become thin and flat in mature flowers although never exceeding .5 millimeter in length. In perfect flowers the anthers are borne on short filaments, about one-third or less the length of the anthers. In other respects the flower morphology corresponds to that which is general for funcus, i.e., tricarpellate ovary, 3 sepals and 3 petals (Buchenau 1906). Inflorescences of pistillate and perfect flowers may occur intermixed in the marsh due to interweaving of the rhizomes, or they may occur in pure stands. The observations and data presented herein may further serve to explain, in part, the inconsistent descriptions of floral morphology by previous authorities.

LITERATURE CITED BUCHENAU, F. 1906. Juncaceae. In Engler. Das Pflanzenreich, 25(IV. 36): 1-284. CHAPMAN, A. W. 1897. Flora of the Southern United States. Cambridge, Mass., 3rd Ed., 520 p. CORRELL, D. S. AND M. C. JOHNSTON 1972. Manual of the Texas Flora. Texas Research Foundation, 1881 p. 1974J Eleuterius: Flower Morphology of funcus roemerianus 497

ELEUTERIUS, L. N. 1972. The marshes of Mississippi. Castanea, 37: 153-168. (In preparation). An autecological study of Juncus roemerianas. ENGLEMANN, GEORGE 1868. A revision of the North American species of the genus JUIlCUS. Transactions of the Academy of Science of St. Louis, 2: 424-498. FERNALD, MERRITT L. 1950. Gray's Manual of Botany. 8th Ed., American Book Company. New York, 1632 p. GLEASON, HENRY A. 1952. Illustrated flora of the northeastern United States and adjacent Canada, 3: 482 p. The New York Botanical Garden. New York. LONG, R. AND O. LAKELA 1972. Manual of the flora of Tropical Florida. University of Miami Press. Coral Gables, Florida, 692 p. RADFORD, A. E., HARRY E. AHLES AND C. RITCHIE BELL 1968. Manual of the vascular flora of the Carolinas. Univ. North Carolina Press. Chapel Hill, North Carolina, 1183 p. SCHEELE, ADOLPH 1849. Junceae. 1. Juncus roemerianus. Linnaea, 22: 348. SEIBERT, ROLAND WILLIAM 1969. Flowering patterns, germination and seed and seedling development of Juncus roemerianus. Ph.D. dissertation. North Carolina State University, Raleigh, N. C., 43 p. SMALL, J. K. 1903. Flora of the Southeastern United States. New York, 256 p. (Pub- lished by author). 1933. Flora of the Southeastern United States. North Carolina Press. Chapel Hill, N. C., 1554 p.