Word of the Week: Filament

filament [ filuh-muhnt ] noun: the stalk that supports the pollen bearing anther in the male reproductive organ (stamen) of a flower; a long strand of similar cells joined end to end, as found, for example, in certain bacteria, algae, and fungi

A flower of native Actaea racemosa (common black cohosh) has 55–100 fertile stamens, which are anthers held by filaments. Here a raceme of flowers is attended by a bumble bee and a hovering syrphid fly in July. Photo © Mary Free

For gardeners, the most common encounter with the word filament is in naming the reproductive parts of flowers. The word comes from the Latin filum, meaning “thread,” and aptly describes the thin, usually springy stalks holding up the anthers.

Tradescantia virginiana (spiderwort) is a familiar three-petaled flower that blooms purple/lavender, pink, white, or blue in many of our gardens. Some say the common name comes from the viscous fluid secreted by the cut stems–as it dries, it hardens into silky threads like spider webs; or perhaps the delicate spiderweb-like filaments. The long hairs (beards) of the filaments may serve a reproductive function, for example attracting insects “either toward or away from the main source of pollen.” (Faden, 1992)

The six filaments of native Tradescantia subaspera (zigzag spiderwort) are covered with long, purple, segmented hairs. Photo courtesy of Jim Conrad

Spiderworts have another distinction: The filament hairs of some cloned (not wild) spiderworts indicate the likely mutagenicity of low levels of radiation by turning from purple-blue to pink. Experiments testing this have been conducted around nuclear plants including in Japan and around Chernobyl. The color is easily observed through a microscope due to the size and nature of the hair cells, which resemble beads in a chain (moniliform), although “they were never sensitive enough to be useful indicators” of abnormal radiation according to Robert Faden, Research Botanist Emeritus at the Smithsonian Institution’s National Museum of Natural History.

The term filament also describes the threads peeling off the leaf margins of a plant like Yucca filamentosa (common yucca) as reflected in its epithet. In Cotinus coggyria (smoketree), what most of us call the flowers are actually filaments (some botanists call them hairs in this case) among the tiny, inconspicuous yellow flowers that soon disappear, leaving large panicles of pink filaments resembling airy blooms. Passiflora incarnata (purple passionflower) is a flower much enhanced by long, showy, purple and white filaments (Flora of Virginia labels them a fringe) that grow around its corona and may serve as nectar guides.

Click on images  for larger views and captions.

The term filament is also used to describe the rhizoids that anchor mosses to the trees, rocks or other surfaces where they grow and do not have a reproductive function. Young moss has been characterized as “a tangled mass of branching green filaments.” (McCune & Whitbeck) Likewise, the term fungal filaments describes rhizines, which attach foliose lichens to their substrates.

Gardeners with ponds or other water features in their gardens may also see the adjectival form of the term applied to filamentous algae, which differ from the free-floating one-celled or planktonic algae we see in other bodies of water. Filamentous algae can be a problem in shallow ponds with too many nutrients flowing in and too much sun, causing the water to turn an unhealthy and murky green or coated with floating strands of green vegetation, emitting odors and depleting oxygen as it decays.

References

Faden R. 1992. Floral Attraction and Floral Hairs in the Commelinaceae. Annals of the Missouri Botanical Garden. 79(1): 46-52. DOI:10.2307/2399808

McCune B, Whitbeck K. Living in the Land of Mosses. Pacific Northwest Plant Disease Management Handbook © Oregon State University. [accessed 22 June 2021]

Plant Database. Tradescantia virginiana. Lady Bird Johnson Wildflower Center. [accessed 22 June 2021].

Sallenave R. Revised 2017. Managing Filamentous Algae in Ponds. Guide W-103. 

College of Agricultural, Consumer and Environmental Sciences, New Mexico State University.

Weakley AS, Ludwig JC, Townsend JF. 2012. Flora of Virginia. Botanical Research Institute of Texas. pages 772, 1008.

Webster B. April 25, 1979. Flower is Detector of Slight Radiation. The New York Times. Section A, page 24.

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