ON SPECIES OF THE SEAGRASS, , IN !

RONALD C. PHILLIPS Department of Botany, Seattle Pacific College, Seattle 19, Washington

ABSTRACT Three vegetative leaf characters previously used to separate species of the seagrass, Halodule Endlicher, are shown to vary on the same , and also on in different environments, to such a degree that they cannot be used as species characters. These characters are: leaf width, apex morphology, and the presence or absence of lacunae around the mid- vein. It is the opinion of the writer that all Halodule plants which he has seen from Florida waters belong to H. wrightii Ascherson.

INTRODUCTION Despite the historical use of floral morphology as the basis for the sepa- ration of species of vascular plants, leaf characters have been used to dis- tinguish species of Halodule Endlicher, because of the rarity of flower pro- duction. Three leaf characters have been used: width; presence or absence of lacunae around the midvein; and morphology of the mature tip (mainly whether bidentate or tridentate) (Sauvageau, 1890; Feldmann, 1938; den Hartog, 1960, 1964). In a previous study of Florida seagrasses, Phillips (1960) found that the leaves of Halodule wrightii Ascherson varied with the environment. It was suggested by den Hartog (1964) that two species were present in Florida, rather than a variation in one species. Later, in an experimental planting of Zostera marina L. in Puget Sound, Washington, the writer observed (unpublished data) extensive variation among the leaves of this seagrass in relation to its environment. Recently den Hartog (1964) described three new species of Halodule from Pacific Central America, using leaf morphology as the principal basis for their separation: H. beaudettei (den Hartog) den Hartog, H. bermuden- sis den Hartog, and H. ciliata (den Hartog) den Hartog. There have been no studies, as far as the writer is aware, concerning the degree of variation in leaf morphology in H. wrightii. Therefore, it seemed worthwhile to undertake a study of the leaves of Florida Halodule, in order to decide whether plants in that area represent one species or more than one species, as den Hartog has suggested.

METHODS AND MATERIALS Collections of Halodule wrightii from Point Pinellas, near St. Petersburg, Florida, were preserved in formalin, and kindly sent to the writer by Mr.

1 Contribution No. 106 from the Florida State Board of Conservation Marine Laboratory, Sl. Petersburg. 1967] Phillips: Halodule in Florida 673 TABLE 1 NEW WORLD SPECIES OF Halodule (Data Taken from den Hartog, 1964) Species Tidalzone Leaf width Leaf length Leafapex H. wrightii Upper part 0.33-0.8 mm 5-18 em Bidentate of sublit- toral H. beaudettei Sublittoral 0.67-1.25 mm 1.5-6 em Tridentate (median tooth 1-10 times as long as lateral teeth) H. bermudensis Sublittoral 0.67-1.25 mm 2.5-5 (20- Bidentate 25) em H. ciliata Not men- 0.5-1.0 mm 5-6 em Mostly bidentate tioned but length of me- dian tooth vari- able

K. D. Woodburn of the Florida State Board of Conservation Marine Labo- ratory. Mr. Woodburn made these collections on 30 November, 1964, from three different tidal levels : Zone 1, exposed at neap ; Zone 2, ex- posed only at spring low tides; Zone 3, sublittoral (never exposed). In studying this material, only mature leaves were used, as den Hartog (1964) pointed out that leaf-tip morphology changed as the leaves matured. The leaves of H. wrightii possess three veins or vascular bundles, one cen- tral and two lateral. Each vein may produce an extension at the leaf tip, in the form of a tooth. If all three of the veins produce extensions, the leaf tip is tridentate; if only the two lateral veins are extended, the leaf is bi- dentate. The median dentation is the most variable one in length.

RESULTS Table 1 is an assessment of New World species of Halodule. Leaf Tips.-Immature or young leaves of H. wrightii from Point Pinellas all possessed a tridentate tip, regardless of the tidal zone from which they came. Mature leaves from Zone 1 ranged from bidentate to semi-tridentate (with a short median tooth). There was as much variation among leaves from a single as there was among leaves from different , which may have come from different plants (Fig. 1). Mature leaves from all three tidal zones exhibited apices ranging from bidentate to tridentate. The bidentate condition was predominant in Zone 1, and no leaves were seen in which the median tooth was as long as (or 674 Bulletin of Marine Science [17(3)

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rjt1 1m ro Em (2) DIU clU itlm FIGURES1-3.-FIGURE 1. Specimens from Tidal Zone 1. A, Rhizome 1: (1) Plant 1,* immature leaf 1.0 em long; (2) Plant 1, mature leaf 3.5 em long; (3) Plant 2, mature leaf 3.8 em long; (4) Plant 3, mature leaf 2.7 em long; (5) Plant 4, mature leaf 3.2 em long. B, Rhizome 2: (1) Plant 1, mature leaf 2.9 em long; (2) Plant 2, mature leaf 3.2 em long; (3) Plant 3, mature leaf 2.3 em long; (4) Plant 4, mature leaf 3.4 em long.-FIGURE 2. Specimens from Tidal Zone 2. A, Rhizome 1: (1) Plant 1, immature leaf 5.1 em long; B, Rhizome 2: (1) Plant 1, mature leaf 10.0 em long; (2) Plant 2, mature leaf 7.0 em long; C, Rhizome 3: (1) Plant 1, mature leaf 6.6 em long; (2) Plant 2, mature leaf 7.6 em long; (3) Plant 3, mature leaf 8.7 em long; D, Rhizome 4: (1) Plant 1, mature leaf 7.9 em lang.-FIGURE 3. Specimens from Tidal Zone 3 (no leaf measurements taken from the longest leaves, as most were with- out the tip; tip measurements taken from longest leaves possible). A, Rhizome 1: (1) Plant 1, immature leaf 1.3 em long; (2) Plant 2, mature leaf 4.7 em long; (3) Plant 3, mature leaf 5.8 em long; B, Rhizome 2: (1) Plant 1, mature leaf 3.4 em long; (2) Plant 2, mature leaf 5.3 em long; C, Rhizome 3: (1) Plant 1, mature leaf 12.1 em long; (2) Plant 2, mature leaf 4.7 em long; (3) Plant 3, mature leaf 8.2 em long. longer than) the lateral teeth, thus the range was from bidentate to semi- tridentate. In Zone 2, the median tooth was sometimes the longest, and the majority of leaf tips were either semi-tridentate or fully tridentate (Fig. 2). In Zone

• As used here, "plant" refers to an erect branch with leaves. 1967] Phillips: Halodule in Florida 675 3, the tridentate condition was predominant, as the majority of leaf tips had the median tooth longer than the lateral teeth (Fig. 3). One mature leaf was bidentate. Leaves from Zone 2 were thus intermediate between those from Zones 1 and 3. Leaf Lengths.-In Zone 1, leaf lengths ranged from 2.3 to 5.7 cm; in Zone 2, from 6.6 to 10 cm; in Zone 3, the average length was greater than that in Zone 2, but exact measurement of many of the leaves was not possi- ble because their tips were missing, probably as a result of grazing by ani- mals. Thus, the average length of the leaves increased with mean depth. Leaf Width.-In Zone 1, leaf widths ranged from 0.33 to 0.55 mm; in Zone 2, from 0.60 to 0.75 mm; in Zone 3, from 0.60 to 1.0 mm. As with leaf length, the average width of mature leaves increased with mean depth. No variations were found in rhizome or root anatomy in the collection studied. DISCUSSION The plants from Point Pinellas which were studied by the writer are re- garded as typical H. wrightii, as are those in all other collections of this genus which he has seen from Florida waters. The degree of variation ex- hibited by the leaves in the Pinellas Point collection, not only by those from different environments but even by those on the same rhizome, indicates that the characters of leaf morphology considered above do not furnish a valid basis for the separation of species. A similar conclusion was reached by den Hartog (1964) and Phillips (1960) concerning the presence or ab- sence of lacunae around the leaf midvein, a character used by Sauvageau (1890) and Feldmann (1938), who also used leaf-tip morphology, to separate H. wrightii and H. uninervis. The results of this study show that the range of variation for leaves of H. wrightii near St. Petersburg is great enough to include both H. wrightii and den Hartog's H. beaudettei, especially in tidal zone 3, and that up to the present time H. wrightii is the only adequately described species of Halodule in Florida waters.

ACKNOWLEDGMENT Grateful acknowledgment is made to Dr. R. F. Scagel for use of the herbarium at the University of British Columbia, and to Dr. H. J. Humm for reading the manuscript and making helpful suggestions.

SUMARIO SOBRE ESPECIES DE LA YERBA MARINA Halodule EN LA FLORIDA Tres caracteres vegetativos de la hoja previamente usados para distinguir especies de la yerba marina Halodule Endlicher se demuestra que varian en la misma planta y tambien en plantas en ambientes diferentes, a tal extremo que no pueden ser usados como caracteres espedficos. Estos 676 Bulletin of Marine Science [17(3) caracteres son: ancho de la hoja, morfologfa del ipice y la presencia 0 ausencia de lagunas alrededor del nervio central. Es opinion del que escribe que todas las plantas Halodule de las aguas de la Florida que el ha vista pertenecen a H. wrightii Aschersan. LITERATURE CITED

FELDMANN, J. 1938. Sur la repartition du Dip/anthera wrightii Aschers. sur la cote occi- dentale d'Afrique. Bull. Soc. Hist. Nat. Afr. N., 29: 107-117. HARTOG, C. DEN 1960. New seagrasses from Pacific Central America. Pac. Nat., 1 (15): 1-8. 1964. An approach to the of the seagrass genus Halodu/e End!. (Potamogetonaceae). Blumea, 12: 289-312. PHILLIPS, R. C. 1960. Environmental effect on leaves of Dip/anthera Du Petit-Thouars. Bull. Mar. Sci. Gulf & Carib., 10: 246-253. SAUVAGEAU, C. 1890. Sur la structure de la feuille des genres Halodule et Phyllospadix. louro. de Bot., 4: 321-334.