Feature Plant
Manitoba maple
(Acer negundo)
Photo by L. Kershaw
For most Alberta plants, the process of growing and flowering through the summer culminates in the setting of seed. Once the seeds are ripe comes the next challenge: how to disperse them in an efficient manner. The answers that plants have come up with to meet this challenge are many and varied.
There are the burr-coated seeds of species like bluebur (Lappula squarrosa) and common burdock (Arctium minus) - hmmm some similarities in names. These rely on sticking to the coat (or in my case socks and shoe laces) of a passing animal, in the hopes that when the seeds fall or are pulled off, some at least will land in a new and suitable habitat. And of course coconuts are the kings of floating seed dispersal (not an Alberta species, but a good example).
One of the most fascinating strategies is the helicopter approach. The seeds of species such as Manitoba maple (Acer negundo) autorotate as they fall from the tree. According to a recent article in Science, they “generate unexpectedly high lift…by generating a stable leading-edge vortex (LEV) as they descend.” This allows autorotating seeds to stay longer in the air than non-autorotating seeds. The advantage? The longer in the air, the further the seeds are likely to be carried, out of the shadow of the parent and, with luck, to new and possibly suitable habitats. The study found that autorotating seeds fall at 1 m/sec or less, so ... with a 10 km/hr wind, about 3 m/sec, the seed from a 10 m high branch could travel 30 m ... almost 100 ft., carrying these relatively heavy seeds well away from the shade of the parent. This will come as no surprise to any gardener whose neighbors have female Manitoba maples.
The study concludes “LEVs also explain the high lift generated by hovering insects, bats, and possibly birds, suggesting that the use of LEVs represents a convergent aerodynamic solution in the evolution of flight performance in both animals and plants.”
"Dust particles reveal airflow around a falling samara, showing leading edge vortex." from Letink et al. 2009
Reference Cited
Leading-Edge Vortices Elevate Lift of Autorotating Plant Seeds D.
Lentink,1,* W. B. Dickson,2 J. L. van Leeuwen,1 M. H. Dickinson2
Science 12 June 2009:
Vol. 324. no. 5933, pp. 1438 – 1440
DOI: 10.1126/science.1174196
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AB Digital Flora — Special ANPC Offer!
‘Flora ID Northwest’ has completed a digital key containing complete descriptive information and photographs for all vascular plant species known to grow in Alberta. The key is interactive, allowing you to identify species in a few simple steps using almost any plant features.
- Definitions of terms are provided, illustrated with line drawings
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- Technical botanical terms are kept to a minimum
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For more details, please see the attached article and the upcoming IRIS.
