Dendrolycopodium hickeyi (Hickey's Clubmoss)
|Also known as:||Hickey's Tree Clubmoss, Pennsylvania Clubmoss, Princess Pine|
|Habitat:||part shade, shade, sun; average to dry sandy soil; deciduous, mixed and conifer forest, forest edges and openings|
|Fruiting season:||August - October|
|Plant height:||4 to 12 inches|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Leaves and stems:
Leaves are evergreen, alternate but spirally arranged with 6 leaves in a cycle, appearing as 6 columns when viewed from the side of the stem (6-ranked), and round in cross-section (like a bottle brush). Leaves are about ¼ inch (2.5 to 5.5 mm) long, to 1.2 mm wide, linear, medium green, toothless, and lacking a hair-like or spine-like tip. Horizontal stems run underground. At fairly regular intervals, erect shoots emerge, each with 2 to several fanning, spreading to ascending branches and appearing tree-like. Leaves along the lateral branches are appressed to ascending, those on the vertical stem between the branches are usually more tightly appressed. Erect shoots are up to 12 inches tall but more typically about half that. Each year's new growth is not marked by a distinct constriction.
Spores develop in spike-like or cone-like structures called strobili. Strobili are stalkless, single at branch tips, and ½ to 2½ inches long, usually 1 to 7 clustered at the top of the plant and occasionally a few in the lateral branches. Each tiny spore sac is attached to a scale (sporophyll) that is about 1/8 inch (3.5mm) long, triangular to tear-drop shaped and tapering to a slender, sharply pointed tip. Scales are initially light green and tightly appressed, turning yellowish as they mature and light brown when dry, then become more spreading to release the spores in late summer into fall. The strobili persist through winter.
Hickey's Clubmoss is occasional in Minnesota's forests from the Twin Cities north. It is among the species formerly all lumped into Lycopodium (L. dendroidium), which many references have now split into several genera and we have followed suit. Distinguishing characteristics of the new groups are: whether spores develop in cone-like strobili or in leaf (or leaf-like) axils, whether strobili are stalked or stalkless, whether horizontal stems are above or below ground, whether branching on erect shoots is tree-like or not, the number of leaves in a spiral cycle, whether leaves are scale-like or not and whether they have a hair-like tip. The Dendrolycopodium species all have stalkless, cone-shaped strobili, underground stems, 6-ranked leaves that are not scale-like and lack a hair-like tip, and have a tree-like form like little spruce trees, so are often commonly referred to as ground-pines. Hickey's Clubmoss also has 1 to 7 stalkless strobili at the top of the plant, sometimes also a few in the lateral branches, leaves along the erect shoots between the branches are mostly appressed, and branches are round in cross-section like a bottle brush.
Of the other Dendrolycopodium species in Minnesota, Tree Clubmoss (Dendrolycopodium dendroidium) has widely spreading leaves on the vertical stem between the branches. A third species, Flat-branched Tree Clubmoss (D. obscurum), which may or may not be present in Minnesota, has leaves of varying sizes, the one on the back of the branch stem distinctly shorter, and it and the leaf opposite to it are appressed, which gives the branch a more flattened shape in cross-section. These 3 were once considered variations of the same species, Lycopodium obscurum, and all commonly called Princess Pine in various references. Of note is that much attention is given to the exact leaf spacing arrangement of these 3 species, but the differences between D. dendroidium and D. hickeyi are quite subtle and not always helpful in the field. Compare with other clubmosses with cone-like strobili: Spinulum species have stalkless strobili but lack tree-like branching, Lycopodium have stalked strobili and leaves with hair-like tips, and Diphasiastrum have stalked strobili and scale-like leaves. While several different clubmoss species may grow side by side, hybridization is not common.
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- Hickey's Clubmoss plant
- Hickey's Clubmoss plant
- Hickey's Clubmoss plants
- vegetative plants
- Hickey's Clubmoss habitat
- Hickey's Clubmoss on Lake Superior's north shore
- maturing strobili
- old strobili
- comparison of D. dendroidium and D. Hickeyi leaf arrangement
Photos courtesy Peter M. Dziuk taken in Anoka, Carlton and Lake counties.
Have you seen this plant in Minnesota, or have any other comments about it?
on: 2021-04-26 15:36:38
In the Superior National Forest, I have checked many a tree clubmoss and they've all been D. dendroidium. It got to the point where I was doubtful D. hickeyi even existed, until one day in the Chippewa NF, I finally came upon a single individual of one. It was a momentous day!