alate [ EY-leyt ] adjective: winged
When you hear the word wings, you probably visualize birds, insects, or planes. Unless you are a botanist or an avid gardener, plants are not images that you first call to mind. However, some plant species have alate or winged parts.
Plants With Alate Fruit/Seeds
Left to right: Acer rubrum, Betula nigra, Liriodendron tulipifera, Ulmus parviflora, Ailanthus altissima.
Consider Acer (maple) trees and their samaras—achenes with a membranous wing at one end. Other species with samaras or alate seeds include ash, birch, native Liriodendron tulipifera (tuliptree), elms, invasive Ailanthus altissima (tree of heaven), and some conifers like pines, firs, and hemlocks. Although the wing designs may differ from species to species, these wings have one thing in common: they are created for flight.
The aerodynamics of a maple samara is similar to that of a helicopter descending without engine power. The wing-like tissues, which surround the achenes of elms and tree of heaven, cause their seeds to flutter or spin through the air. Winged seeds released by strobili can travel long distances. “The natural reforestation of conifers following fire is proof of the flying ability of seeds from nearby forested slopes” (Armstrong 2001). No matter their design, the function of these wings is to use the air currents to carry their seeds far from the mother plant to increase the odds of perpetuating their species.
Plants With Alate Petioles and Rachises
Left to right: Rudbeckia fulgida var. sullivantii ‘Goldsturm,’ Symphyotrichum prenanthoides, Verbesina virginica, Onoclea sensibilis, Rhus copallinum.
However, there are other winged plant parts that have nothing to do with flight. Some plants, like herbaceous natives Rudbeckia fulgida (orange coneflower), Symphyotrichum prenanthoides (crooked-stem aster), and some Verbesina (crownbeards) or natives Onoclea sensibilis (sensitive fern) and Rhus copallinum (winged sumac) have leaves with alate petioles or alate rachises (main axis of a frond or compound leaf).
Plants With Alate Stems
Still others have alate stems. Herbaceous plants with winged stems include annual Limonium sinuatum (statice) and natives Helenium flexuosum (purple-headed sneezewood) and Verbesina. The epithet of statice, sinuatum, refers to the wavy margins along its stem’s three wings. The stems of Verbesina alternifolia (wingstem or yellow ironweed) usually have wings but sometimes not. Flora of Virginia describes the stems of V. occidentalis (yellow crownbeard) and V. virginica (white crownbeard or frostweed) as 4-winged and narrowly or interruptedly winged below, respectively, with both having leaves with winged petioles (often) decurrent on the stem—that is thin strips of leaf blade tissue run down the stem to the leaf below. As an aside, since this occurrence has nothing to do with its wings, the stems of frostweed can split in winter due to expanding and contracting sap, which when released freezes in the frigid air, drawing up more and more sap that seeps out and freezes forcing the previously formed ice crystals outward resulting in ice ribbons and other unique shapes along the stem (Vogelpohl 2013).
Left to right: Limonium sinuatum, Helenium flexuosum, Verbesina alternifolia, Verbesina virginica (alate stem and with ice formations), Euonymus alatus, Liquidambar styraciflua, Ulmus alata.
Woody plants with alate stems include invasive Euonymus alatus (winged euonymus, burning bush) and natives Liquidambar styraciflua (sweetgum) and Ulmus alata (winged elm), both of which also have winged seeds. In winged euonymus, cork cell activity is localized in a regular and uniform pattern with wedge-shaped wings developing in longitudinal grooves on first year stems. For two to three years the wings elongate at the base while the stems thicken; then the wing growth stops and eventually, with continued exposure to the elements, the wings fall off the stem (Bowen 1963). The irregular, corky wings of sweetgum tend toward one-sided growth, appearing mostly on the upper side of lateral branches. Two wings develop on opposite sides of the stems of winged elm when its cork splits longitudinally in its first year. The wings persist but do not enlarge proportionate to the stem’s growth over time (Gregory 1888).
Do the alate parts of petioles and stems serve a practical purpose as do the wings on seeds? John Nelson, the retired curator of the A. C. Moore Herbarium at the University of South Carolina, concedes that the reason a plant like Ulmus alata “would go through the trouble of making such wings” is not understood as “wings have no known functional value for the plant.” So, it appears that for some plants, researchers are still pondering that question.
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References
Armstrong WP. 2001. Blowing In the Wind. Seeds & Fruits Dispersed By Wind. Wayne’s World: 9 May 2001. (accessed October 22, 2022).
Bowen WR. 1963. Origin and Development of Winged Cork in Euonymus alatus. Botanical Gazette, 124(4), 256–261.
Gregory EL. 1888. Development of Cork-Wings on Certain Trees. I. Botanical Gazette, 13(10): 249–258.
Gregory EL. 1889. Development of Cork-Wings on Certain Trees. V Botanical Gazette, 14(2): 37-44.
Lentink D. 2009. Maple Seeds and Animals Exploit the Same Trick to Fly. California Institute of Technology. (accessed January 9, 2021).
Nelson J. November 26, 2021. Why the winged elm has wings is one of nature’s puzzles | Mystery Plant. Home & Garden. Tallahassee Democrat.
Nickrent DL. Lecture 14. Periderm. Plant Biology Program. Southern Illinois University. (accessed October 22, 2022).
Vogelpohl S. November 16, 2013. Know Your Natives – Frostweeds “Bloom” Frost Flowers. Arkansas Native Plant Society.
Vogelpohl S. November 13, 2015.. Know Your Natives – Yellow wingstem. Arkansas Native Plant Society.
Weakley AS, Ludwig JC, Townsend JF. 2012. Flora of Virginia. Botanical Research Institute of Texas.