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Aquatic and Wetland Vascular Plants of the Northern Great Plains

Myriophyllum L. -- Water milfoil


Rooted aquatic or amphibious perennials with flexuous submerged stems and mostly whorled leaves, these pinnately divided into filiform segments. Flowers small, sessile in the axils of the upper reduced leaves or bracts, also usually subtended laterally by a pair of minute bracteoles, emersed at anthesis, in terminal, interrupted spikes. Flowers imperfect or perfect, the male flowers above the female in the spike, with perfect flowers, if any, in the middle portion of the spike; calyx inconspicuous, 4-parted in the male flowers, appressed to the ovary and minutely 4-toothed at the summit in female or perfect flowers, the teeth usually deciduous in fruit; corolla of 4 membranous petals, reduced or absent in female flowers; stamens 8 or 4; pistil 4-carpellary, stigmas 4, sessile or nearly so, papillose-tufted, ovary inferior, 4-celled. Fruit nutlike, 4-lobed, eventually splitting into 4 mericarps.

References:

Aiken, S. G.  1981.  A conspectus of Myriophyllum (Haloragaceae) 
     in North America.  Brittonia 33:57-69.

Love, A.  1961.  Some notes on Myriophyllum spicatum.  Rhodora 	
     63:139-145.

Nichols, S. A.  1975.  Identification and management of Eurasian water 	
     milfoil in Wisconsin.  Trans. Wisconsin Acad. Sci. 63:116-128.
Patten, B. C., Jr. 1954. The status of some American species of Myriophyllum as revealed by the discovery of intergrade material between M. exalbescens Fern. and M. spicatum L. in New Jersey. Rhodora 56:213-225.

Lead Characteristic Go To
1 Upper floral bracts entire; lower bracts entire, serrate or pinnatisect, not more than 2X longer than their subtended flowers. M. exalbescens
1 Upper floral bracts entire to serrate or pinnatisect; lower bracts serrate or pinnatisect, usually more than 2X longer than their subtended flowers. Lead 2
2 Upper bracts shorter than or equaling their subtended flowers, only the lower bracts exceeding their flowers; stamens 8. M. verticillatum
2 All bracts conspicuously exceeding their subtended flowers; stamens 4. Lead 3
3 Bracts laminate, mostly oblong-lanceolate to ovate-lanceolate, pectinate below to serrate above in the spike, the lowermost distinctly different from the foliage leaves. M. heterophyllum
3 Bracts not laminate, mostly linear, finely pinnatisect below to pinnatifid or shallowly toothed to subentire above in the spike, the lowermost similar to the foliage leaves. M. pinnatum


29. Haloragaceae, the Water Milfoil Family
1. Myriophyllum L. -- Water milfoil
1. Myriophyllum exalbescens Fern.
2. Myriophyllum heterophyllum Michx.
3. Myriophyllum pinnatum (Walt.) B.S.P.
4. Myriophyllum verticillatum L.


Return to Family -- Haloragaceae - The Water Milfoil Family
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