Natural Sciences Department, Oral Roberts University, Tulsa, Oklahoma 74171
A taxonomic imbroglio exists in the genus Myriophyllum, particularly with respect to the taxa Myriophyllum spicatum L., Myriophyllum exalbescens Fern., and Myriophyllum verticillatum L. Myriophyllum spicatum and M. verticillatum were first described by Linnaeus in the 1700's (1). In 1919, Fernald (2) described a new species for North America, Myriophyllum exalbescens.
Jepson (3), Hulten (4), Patten (5, 6), Nichols (7), Brooks and Hauser (8), and Orchard (9) found the differences between M. spicatum and M. exalbescens too insignificant to warrant separation. Hulten and Patten submered exalbescens within the older taxon as a subspecies, whereas Jepson, Nichols, Brooks and Hauser, and Orchard preferred the varietal level. Fernald (10) steadfastly opposed considering M. spicatum and M. exalbescens as one species.
Love (11), Reed (12), Aiken (13), Aiken and Walz (14), Aiken et al. (15), and Aiken (16) agreed with Fernald. They concluded that M. spicatum and the native American species, M. exalbescens and M. verticillatum, should be separate taxa based on differences in morphology, physiology, and phenology. Reed (12), Aiken and Walz (14), and Aiken (16) noted that M. exalbescens and M. verticillatum are distributed only north of the 0 C January isotherm required for vernalization and successful turion formation in these taxa (13, 17, 18, 19). In contrast, M. spicatum occurs farther south. Except for unusually cold winters and perhaps for the high elevations of northwest Cimarron County, Oklahoma is not cold enough for the persistence of M. exalbescens and M. verticillatum. Nevertheless, numerous specimens deposited in Oklahoma herbaria were identified as these two species. This discovery led us to study the genus Myriophyllum.
Field studies were conducted throughout Oklahoma during the summers of 1979-1981. Plants were collected and specimens on deposit in State herbaria were examined. The Myriophyllum sheets were examined carefully and compared with reference specimens and monographic descriptions (13, 20, 21). This study revealed that all specimens identified as M. exalbescens or M. verticillatum were M. spicatum or M. heterophyllum.
Only four species of the genus Myriophyllum exist in Oklahoma. There are two native species: M. pinnatum (Watt.) BSP. and M. heterophyllum Michx., and two introduced species: M. aquaticum (Vellozo) Verdcourt and M. spicatum L.
Partial support for this research was provided by Contract No. DACW56-80-C-0025 from Tulsa District, U.S. Army Corps of Engineers. Dr. Ronald Tyrl, Oklahoma State University, provided advice and encouragement. We appreciate the aid of Dr. Susan Aiken of the Biosystematic Research Institute in Ottawa, Ontario, in annotating our Myriophyllum collection and reviewing this manuscript.
1. S. G. AIKEN and J. McNEILL, Bot. J. Linnean Soc. 80: 213-222 (1980).
2. M. L. FERNALD, Rhodora 21: 120-124 (1919).
3. W. L. JEPSON, A Manual of the Flowering Plants of California. Assoc. Students Store, Univ. of Calif., Berkeley, CA, 1925.
4. E. HULTEN, Arsskr. N. F. Avd. 2. 43(1): 1067-1200 (1947).
5. B. C. PATTEN, JR., Rhodora 56: 213-225 (1954).
6. B. C. PATTEN, JR., Bull. Torrey Bot. Club 83: 5-18 (1956).
7. S. A. NICHOLS, Trans. Wis. Acad. Sci. Arts Lett. 63: 116-128 (1975).
8. R. E. BROOKS and L. A. HAUSER, Aquatic Vascular Plants of Kansas I: Submersed and Floating Leaved Plants, Technical Publ. No. 7, State Biol. Survey of Kansas, 2045 Avenue A, Campus West, Lawrence, KS, 1978.
9. A. E. ORCHARD, Brunonia 4: 27-65 (1981).
10. M. L. FERNALD, Rhodora 47: 218 (1945).
11. A. LOVE, Rhodora 63: 139-145 (1961).
12. C. F. REED, Phytologia 36: 417-436 (1977).
13. S. G. AIKEN, North American Myriophyllum (Haloragaceae). Ph.D. Dissertation, Univ. of Minnesota, St. Paul, MN, 1979.
14. S. G. AIKEN and K. F. WALZ, Aquatic Bot. 6: 357-363 (1979).
15. S. G. AIKEN, R. R. NEWROTH, and I. WILE, Can. J. Plant Sci. 59: 201-225 (1979).
16. S. G. AIKEN, Brittonia 33(l): 57-69 (1981).
17. J. A. WEBER, Mich. Bot. 11: 115-121 (1972).
18. J. A. WEBER and L. D. NOODEN, Mich. Bot. 13: 151-158 (1974).
19. J. A. WEBER and L. D. NOODEN, Plant Cell Physiol. 17: 721-731 (1976).
20. D. S. CORRELL and H. B. CORRELL, Aquatic and Wetland Plants of Southwestern United States, Vol. II. Stanford Univ. Press, Stanford, CA, 1978, pp. 1201-1208.
21. W. C. MUENSCHER, Aquatic Plants of the United States. Cornell Univ. Press, Ithaca, NY, 1944, pp. 277-286.