It’s Invasive Species Week 2018 (February 26 – March 2),
which is a great opportunity to learn more about plants by looking at vegetative
villains. Last year we covered what an invasive species is
and why they’re so good at being everywhere (there are levels of invasive-ness
and invasive species have plant superpowers). This year we’ll look at one superpower in
particular: pokiness.
Nothing says DO NOT DISTURB like a thicket of thorns |
This is not the pokey site, instead here's a undisturbed wetland |
1. Disturbance Hypothesis: disturbances that
leave bare ground (e.g. flooding, road building) make great opportunities for
pokey plants to invade.
2. Pokey Hypothesis: once established on bare
ground, pokey plants grow big and dense (pokier) because they aren’t eaten by
animals.
Methods: Looking at the research others have completed on common northern Utah wetland invaders that are also pokey species to see if they support our hypotheses or not. Our invaders of interest in order of pokey length: Russian olive (thorns), Bull thistle (spines), Common burdock (hooks), Roses (prickles), and Stinging nettle (hairs).
Before we gently step into the world of pokey plants I should
explain what we’re talking about. My
trusty plant dictionary [1] doesn’t define ‘pokey,’ it skips from ‘podogyne’
(a structure that supports an ovary) to ‘pollen’
(male gametophytes). However, it does
define spines, thorns, horns, hooked, prickle, process, and many types of hairs
(short, long, stiff, soft, straight, or branching).
Prickles are
small and sharp growths of the epidermis or bark. Sharp parts that come from below the
epidermis are spines and small spines
are called spinules. Thorns
are woody, sharply pointed modified stems. Short, hair-like poking things are called bristles. Not all pokey parts are straight: barbed plants have fish hook-like rigid
barbs, which shouldn’t be confused with hooked
plants, whose pokey parts are bent like hooks, but not as stiff as barbs. All of this is separate from plant surfaces
that aren’t pokey but aren’t smooth, they can be scabrous, siliceous, ribbed, hirsute, or exasperate. In plant terminology spikes are a shape
flowers grow in, not at all involved in the world of pokeys. Pokey is my term for plant parts like bristles,
prickles, spines, thorns, or hooks. Pokey plans are armed plants and the pokeys are
their armature.
Turns out, invasive species are
complicated. While we found some support
for both hypotheses, only Bull thistle supported both because it establishes
quickly on disturbed soil and then grows densely because animals will not graze
it. Burdock will grow well on bare
ground, supporting the first hypothesis, but grazing mammals are willing to
chew it and help disperse seeds. Wild
and livestock animals won’t graze Russian olive or Stinging nettle, allowing them
to grow tall and dense, but neither establishes on bare ground. Invasive roses supported neither of my
hypotheses: they are deliberately introduced and are eaten by many animal
groups.
In conclusion, pokey plant parts are just of the many
features of invasive species that allow them to grow in places they don’t
belong. But now we know some fun facts about invasive species that aren’t
Phragmites.
Methods: Looking at the research others have completed on common northern Utah wetland invaders that are also pokey species to see if they support our hypotheses or not. Our invaders of interest in order of pokey length: Russian olive (thorns), Bull thistle (spines), Common burdock (hooks), Roses (prickles), and Stinging nettle (hairs).
Russian olive - Elaeagnus angustifolia - bigly pokeys called thorns |
Bull thistle - Cirsium vulgare - pretty spine pokeys |
Thorns – the biggest of the pokeys
Well, Russian olive info supports our second hypothesis that being thorny prevents animals from eating you, but fails to support our first hypothesis about disturbance.
Spines – trouble all over
Promising results: Bull thistle is a disturbance-friendly plant that isn't grazed. Both hypotheses supported. Except for bears.
Hooks – able to reach out and grab you
Hmmm. Burdock grows well in disturbed places, but also gets chewed on. Only the first hypothesis on disturbance is supported.
Prickles – adorable term for a painful poke
Shoot. Roses don't support either hypothesis, they don't need disturbance and they're plenty tasty to animals.
Stinging hairs – you won’t even see what’s causing so much pain
Similar to Russian olives, Stinging nettles aren't often chewed on because of their pokeys, but they don't sprout on disturbed ground.
Discussion
Common burdock - Arctium minus - hooked pokeys hitch rides on anything with fur |
Sweetbriar rose - Rosa rubiginosa - a prickle by any other name would still hurt |
Stinging nettle - Urtica dioica - don't walk there! The stinging hairs have histamines in them |
Literature Cited:
[1] Harris, J. G., & Woolf Harris, M. (2009).
Plant Identification Terminology: An Illustrated Glossary. Spring Lake Publishing, Spring Lake, Utah.
[2] Katz, G. L., & Shafroth, P. B. (2003). Biology, ecology and
management of Elaeagnus angustifolia L. (Russian olive) in western North
America. Wetlands, 23(4), 763-777. Available: https://geo.appstate.edu/sites/geo.appstate.edu/files/katz%20and%20shafroth%202003%20biology%20of%20russian%20olive.pdf
[3] Zouhar, Kris. 2005. Elaeagnus angustifolia.
In: Fire Effects Information System, [Online]. U.S. Department of Agriculture,
Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory
(Producer). Available: https://www.fs.fed.us/database/feis/plants/tree/elaang/all.html .
[4] Zouhar, Kris. 2002. Cirsium vulgare. In: Fire
Effects Information System, [Online]. U.S. Department of Agriculture, Forest
Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: http://www.fs.fed.us/database/feis/plants/forb/cirvul/all.html
[2018, February 26].
[5] GROSS, R. S., WERNER, P. A., & HAWTHORN, W. R. (1980). The biology
of Canadian weeds. 38. Arctium minus (Hill) Bernh. and A. lappa L. Canadian Journal of Plant
Science, 60(2), 621-634. Available: http://www.nrcresearchpress.com/doi/pdf/10.4141/cjps80-089
[6] Province of Manitoba. (2017). Common
Burdock. In: Weeds, [Online]. Available: (http://www.gov.mb.ca/agriculture/crops/weeds/common-burdock.html
[7] Richardson, D. M., & Rejmánek, M.
(2011). Trees and shrubs as invasive alien species–a global review. Diversity and distributions, 17(5), 788-809. Available: http://onlinelibrary.wiley.com/doi/10.1111/j.1472-4642.2011.00782.x/full
[8] Munger,
Gregory T. 2002. Rosa multiflora. In: Fire Effects Information System,
[Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain
Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/shrub/rosmul/all.html
[2018, February 27].
[9] Wikipedia. 2018. Urtica dioica. [Online].
Available: https://en.wikipedia.org/wiki/Urtica_dioica
[10] Carey, Jennifer H. 1995. Urtica dioica. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/forb/urtdio/all.html [2018, February 27]