Question: Lincoln, Massachusetts. A survey of nearby wetlands reported Dendrolycopodium obscurum there. This is a drier location. I don't really understand …
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Question
Lincoln, Massachusetts. A survey of nearby wetlands reported Dendrolycopodium obscurum there. This is a drier location. I don't really understand the difference between obscurum and hickeyi.
Answer
Dear jfc, this appears to be Dendrolycopodium obscurum. The difference between it and D. hickeyi are easier to see (at first) when they are both together so the differences are more obvious. In D. obscurum, the trophophylls (i.e., vegetative leaves) on the underside of the lateral branches are shorter and/or more appressed to the branch, so that the overall branch cross-section is elliptic or plano-convex (when you draw a line connecting the tips of the trophophylls to form a polygon). In D. hickeyi, all the trophyophylls on the lateral branches are equal size and have similar orientation, giving the branch a roughly circular cross-section. I don't know if this helps. I have images I can send you directly--feel free to email me and I'll try to make sure you understand these two species.
