trichome
pubescent
tomentous
villous
indumentum
wooly
pilose
colleter
felted
floccose
glochid
hirsute
hispid
hispid
penicillate
puberulose
sericeous
strigose
stellate
arachnoid
How are hairs adventageous to plants? In Johnson (1975)'s review, he concludes that the propensity to make hairs is quite widespread in plants, and suggests that the ability to make hairs is probably genetically available to most plants. Perhaps in line with the Gould Lewontin's famous essay "The Spandrels of San Marcos", Johnson (1975) seems to hint that hairiness in leaves and stems could be just a correlational effect, a trait that exists more due to the need for root hairs than for any function to leaf and stem hairs.
On the other hand, Johnson (1975) reviews quite an array of advantages that have been proposed for leaf and stem hairs. Hairs on leaves may reduce water loss from leaves. Hairs change the reflectance of a leaf, and also the wavelenghts of light absorbed by a leaf. Taking this information together, hairs on leaves could affect leaf temperature, photosynthesis, and water retention. Hairness of plants may make them less palatable to predators (Johnson, 1975). Hairy leaves are not only harder to eat and chew, but they may be less ideal for laying eggs or even for the growth of fungi and bacteria (Johnson, 1975). Finally, Johnson (1975) suggests that hairs on leaves increase the surface area and may influence excretion of gases, fluids, inorganic or organic solutes.
Today I post a picture of lamb's ear, Stachys byzantina . This plant is loved by many gardeners and by my children. Wikipedia suggests that it is native to the middle east. This plant is a member of the Lamiales or Mints. Like other members of the family, Stachys byzantina has a tubular flower, five-fused petals, and a corolla that is bilabiate and appears to have two lips. The bilabiate shape of flowers has evolved more than once so the shape of the flower is perhaps not the best way to identify family. There are many interesting chemicals and oils found in members of the Lamiales, and likewise members of this family are often aromatic. The leaves of members of the Lamiales (including Stachys byzantina ) are often opposite, and the stem is often square. The style of many Lamiales flowers arises from a depression in the ovary.
Click on this picture for a bigger view of Stachys byzantina
Life is busily speeding along, and I can knot afford to spend more than a brief moment on untangling hairy plants; I'm just too harried! (Comb on, there must be better puns for this topic!)
Gould, Steven J and Richard C. Lewontin. 1979. The spandrels of San Marco and the Panglossian paradigm: A critique of the adaptationist programme. Proceedings Of The Royal Society of London, Series B, 205: 581-598.
Johnson, Hyrum B. 1975. Plant pubescence: an ecological perspective. The Botanical Review 41: 233-258.
