Leader for today’s Ramble: Heather Lickliter Larkin
Authors of today’s report: Heather Lickliter Larkin, Linda Chafin
The photos that appear in this report were taken by Heather, unless otherwise credited. Photos may be enlarged by clicking them with a mouse or tapping on your screen.
Nature Ramble rainy day policy: We show up at 9:00am, rain or shine. If it’s raining, we will meet and socialize in the conservatory (bring your own coffee); if there is a break in the rain, we’ll go outside and do a little rambling.
Today’s emphasis: Hydrophobic plants! Hydrophobic means water-repelling, hydro– from the Latin for water and –phobic from Latin for fear.
Number of Ramblers today: 28
Announcements:
The next exhibit to go up in the Garden’s Visitor Center art gallery is entitled “Tiny Worlds.” Five out of six of the artists whose work is in this show are former or current ramblers! Heather Larkin, Don Hunter, Bill Sheehan, Sandy Shaul, Diego Huet, and Rosemary Woodel invite you to appreciate the natural beauty of tiny bugs, fungi, slime molds, and other creatures that are less than 4 inches wide or tall – creatures that most people would normally walk right by. The show will be up from August 18 – November 13. The opening reception is Sunday, August 18, 12 noon – 2:00pm. Food and drink will be available – especially if Ramblers kick in to help Emily organize treats and beverages for the reception! If you can volunteer to help, let Emily know at this email address: egenecarr@me.com
Athens-Clarke County Leisure Services is developing a Master Plan and wants your input! In this quick survey, they want to hear your preferences related to the facilities, programs, and activities managed by Athens-Clarke County Leisure Services. Take the survey here.
The Oconee River Land Trust will hold a herpetology hike on August 24, 2024, from 9:00 a.m –1:00 p.m. for members of the Land Trust. You can join and register for the hike on their website.
Interesting article in the Smithsonian Magazine: Botanists Vote to Remove Racial Slur From Hundreds of Plant Species Names.
Today’s reading: Heather read “The Peace of Wild Things” by poet Wendell Berry.
The Peace of Wild Things
When despair for the world grows in me
and I wake in the night at the least sound
in fear of what my life and my children’s lives may be,
I go and lie down where the wood drake
rests in his beauty on the water, and the great heron feeds.
I come into the peace of wild things
who do not tax their lives with forethought
of grief. I come into the presence of still water.
And I feel above me the day-blind stars
waiting with their light. For a time
I rest in the grace of the world, and am free.
Today’s route: We walked through the Children’s Garden vegetable beds, stopped at the ponds, and then headed to the Visitor Center plaza fountain. From there, we walked through the Herb & Physic Garden and the Heritage Garden, ending at the Sorghum plantings where the cool weather encouraged us to hang out for a while discussing plants and books.
Today’s observations:
Heather opened our hydrophobic exploration by explaining the three ways that water interacts with plant surfaces: “Stop, Drop, and Roll.”
Stop: the plant’s leaves simply get wet, the water staying on the leaves until it evaporates.
Drop: drops of water bead up and eventually drop off the leaves if there are enough of them.
Roll: drops of water immediately roll up into globes and roll off the plant, leaving the surface of the leaf dry. Many plants, especially in the tropics, have specialized “drip tips” on their leaves that help water roll off the leaf.
Rain or dew that falls on the leaves of Purple Basil simply stops then spreads across the leaf surface in a thin sheet and eventually evaporates. Basil originated in dry habitats from central Africa to southeast Asia where evaporation prevents water from lingering on leaf surfaces.
Water forms drops on the surface of this grass leaf.
Small drops of water coalesce into larger drops that roll off the leaf.
Photo by Bill Sheehan
Both hydrophobic strategies – “dropping” and “rolling” – evolved to prevent water from accumulating on plant leaves. There are a multitude of reasons for plants to have developed hydrophobia:
–As drops form and roll off the leaves, they clean the leaves of dust, pollen
grains, and pollutants that block sunlight and limit photosynthesis.
–Dropping and rolling prevents water from blocking stomates, the pores that allow
leaves to take up carbon dioxide and release oxygen.
–Removing water quickly from a leaf inhibits the growth of mold and other pathogens.
–Dropping and rolling moves water off the leaf to the soil and roots before it evaporates.
Water drops have collected debris as they rolled across the surface of this flower.
Bluish green plant surfaces, such as these Parry’s Agave leaves, are due to the waxy coating.
Plants have evolved two types of hydrophobic leaf surfaces: waxy and hairy. A waxy coating on leaves and stems is deceptively smooth to the touch but it is actually minutely textured. The wax surface consists of microscopic towers that prevent water from sticking to the leaf surface and encourages the natural surface tension of the water to curl up on itself, forming a drop. Waxy leaf surfaces serve at least two functions: in aquatic habitats, the wax coating keeps water from sinking leaves; in dry areas, wax prevents water loss from inside the leaf.
Water drops balance on the wax towers like a ball on a comb. Illustration by Wesley Gunn, Science Friday.
The waxy surface eventually wears away on some plants’ leaves, causing older leaves to lose their hydrophobic properties.
Left, a young Tulip Tree leaf has a fresh waxy coating that promotes drop formation. Right, an older Tulip Tree leaf has lost much of its waxy coating and water spreads across its surface.
The hairs on some plants’ leaves work in much the same way: forming a rough texture that suspends water drops and encourages drop formation.
Hairs on the surface of a grass leaf promote drop formation and prevent water from reaching the leaf surface.
Water drops on this leaf surface are supported by tiny branched hairs.
Hydrophobia is not limited to leaves. Hairs on the surface of a tomato plant’s stems, flower stalks, and sepals suspend water droplets and prevent them from spreading across the plant’s surfaces.
The ray flowers on this sunflower head are coated with wax and beaded with water droplets. The leaves were neither hairy nor waxy and the recent rain had coated their surfaces.
Aquatic plants such as lotus, water lilies, and Mosquito Fern are confronted with the constant threat of submersion or swamping by mud and have developed superhydrophobic leaves.
Wax-coated leaves of American Lotus in the Visitor Center Plaza fountain
“Lotus leaves have become an icon for superhydrophobicity and self-cleaning surfaces, and have led to the concept of the ‘Lotus effect’. Although many other plants have super-hydrophobic surfaces with almost similar contact angles, the lotus shows better stability and perfection of its water repellency. (Ensikat et al. 2011. Superhydrophobicity in perfection: the outstanding properties of the lotus leaf. Beilstein Journal of Nanotechnology.)
Lotus leaves repel water.
The floating fronds of Mosquito Fern are thickly covered with hairs that are only 1 or 2 cells thick but are so closely spaced they form a superhydrophobic leaf surface.
In search of more hydrophobic plants, we visited the fountain in the DIG, the Discovery and Inspiration Garden, behind the Porcelain Museum. The fountain was empty but the frogs and toads were there anyway.
(Left to right) Fowler’s Toad, American Bullfrog, and Eastern Spadefoot Toad
Later, a Northern Cardinal joined us in the Sorghum patch as the cooler weather encouraged us to linger and discuss books and plants.
Summary of Observations
Purple Basil Ocimum basilicum ‘Dark Opal’
Tomato Solanum lycopersicum
Parry’s Agave Agave parryi
Mexican Petunia Ruellia mexicana
Swamp Mallow Hibiscus moscheutos var. incana
Sunflower Helianthus sp.
Tulip Tree Liriodendron tulipifera
Water Lily Nymphaea sp.
American Lotus Nelumbo lutea
Mosquito Fern Azolla caroliniana
Smooth Spiderwort Tradescantia ohiensis
Bald Cypress Taxodium distichum
Eastern Tiger Swallowtail Papilio glaucus
Fowler’s Toad Anaxyrus fowleri
American Bullfrog Lithobates catesbeianus
Eastern Spadefoot Toad Scaphiopus holbrookii
Northern Cardinal Cardinalis cardinalis
Joro Spider Trichonephila clavata
Heather shows off her hydrophylic t-shirt.