Rooting About

I'm told that many of you know me well enough not to roll your eyes when you hear me wax lyrical about esoteric subjects such as aquatic plant root differences and such. That's just Debbie, you will say, so here goes with my latest fascination ...

Over the years, I've casually noticed that the roots of our native Myriophyllum verticillatum (whorled water milfoil) on Lake Arrowhead seemed to be different from those of the non-native M. heterophyllum (variable water milfoil) but I've never had concordance from others about this being a known feature despite having remarked on this to quite a few people, nor have I found anything about it in the literature.

As my explorations on the lake are coming to a close with our proposed move, I decided to investigate for myself to satisfy my own burning curiosity, and this is what I have noticed:

The roots on M. verticillatum do not have a branched, filamentous and fibrous look to them - they are mostly single unbranched strands only. I also noted that specimens of M. verticillatum slide very easily out of the substrate as a complete, intact sample, but M. heterophyllum roots require a lot more tugging and manipulation to free them.

M. verticillatum roots

M. heterophyllum roots

Whorled milfoil plant and roots on left and variable milfoil plant and roots on right

As you can see from the two samples, there IS a difference, and this might be even easier to use in the field than counting the number of leaves per whorl and the number of leaflet pairs per leaf, especially since there is overlap between the two.

A single rootlet strand of whorled milfoil (L) next to a single strand of variable milfoil (R)

I'm excited about this - to me, it's a discovery of something undocumented!