Friday, October 9, 2015

Autumn Hitchhiker

A few weeks ago I showed that, though squirrels eat a lot of acorns, they also (unintentionally) plant some.  I gave other examples of "recruiting" animals to carry their children with offerings of tasty fruit.  But fruit costs a plant resources: you have to build that fruit, furnish it with sugar or other desirable food, and then attract animals' attention.  What if plants could get animals' help on the cheap?

Walking the dogs a few days ago, I rediscovered an old friend--and an older enemy--that does just that.

As a boy I often returned from tromping the autumn woods and fields to find my clothes thick with dark, bug-like things.  At first I took them for insects and was eager to get them off!  Soon I recognized them as seeds.  The only way to remove them from a sweater was to disentangle them  one at a time.  And if I'd gone tromping with the dog, so much the worse.  Maddening. 

Yet there was also mystery.  Try as I might, I could never see where they came from.  Sometimes I would watch for their appearance in my clothes to notice where I had picked them up, but they always took me by surprise, and I never discovered their source on my own.  Only years later did I learn the identity of this one of the many Composites* that disperse their young in animal fur.  As its only concession to the need of its children to get away from home, Beggar Ticks (Bidens frondosa) produces a fruit that comes loose at a touch, and has two spines that help it cling to fur or fabric, and is smooth and hard to get hold of. 

I had watched this particular roadside weed off and on for over months.  Then I'd forgotten it.  But walking the dog I happened to glance the right way and caught the plant in the act of readying its trick: preparing to make stowaways of its children.  

I took a photo or two.  Then, on impulse, I offered a sleeve and pants leg for old time's sake.  Those shown were still hanging on when I got home.  I might come to regret this, but I tossed them into the yard.

Bidens frondosa: fall photos show a little bit of how flowers can become hitch-hiking fruits.
 September 27th, 2014

October 19th, 2015

October 10th, 2015.  This plant is a bit behind its neighbor.

The Latin name of the genus, Bidens, means "two-tooth."  
(Think about "bicycle" and "dental.")

*Composite is a venerable but unofficial name for a very large family of flowering plants that bears its flowers in tight clusters that often collectively look like giant single flowers.  Daisy and sunflower are familiar: each has a disk of many, tightly-packed flowers.  Around this are "petals" which, if examined closely, are entire flowers in themselves.  (This seems to be a strategy for attracting pollinators with flowers massed in very visible displays.)  Other Composites (family Asteraceae) you may know include asters, black-eyed Susans, goldenrods, and dandelions, and burs.  Look at one of these closely some time!

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