Sunday, June 12, 2011

Showy Milkweed

What’s blooming in the area: Dr. Huey, wild pink, hybrid tea and miniature roses, buddleia, Japanese honeysuckle, silver lace vine, wide-leaved and red yuccas, lilies, daylily, red hot poker, hollyhock, datura, sweet pea, Jupiter’s beard, alfalfa, brome grass; corn about 6" high.

Beyond the walls and fences: Tamarix, Apache plume, four-wing salt bush, showy milkweed, fernleaf and leatherleaf globemallows, cheese mallow, tumble mustard, alfilerillo disappearing with heat, scarlet bee blossom, white evening primrose, velvetweed, bindweed, gypsum phacelia peaked, woolly plantain, purple mat flower, nits and lice, goat’s head, wild licorice, loco, white sweet clover, western goat’s beard, Hopi tea, native and common dandelions, rice, and three awn grasses; buds on Virginia creeper and stickleaf; needle grass only bloomed along my drive, not in the yard or on the prairie; cottonwood cotton collecting on ground.

In my yard, looking east: Persian yellow rose, raspberry, winecup mallow, coral bells, small-leaved soapwort passing, Bath pinks, snow-in-summer, sea pink, Maltese cross, bouncing Bess, pink evening primrose, pink salvia; buds on baby’s breath; oriental poppy petals had white blotches Monday from whatever blew in from Arizona.

Looking south: Pasture, floribunda and rugosa roses, oxalis, tomatilla.

Looking west: Chives, vinca, Husker red beardtongue, blue flax, catmints, Rumanian sage, flowering spurge; buds on sea lavender.

Looking north: Golden spur columbine, coral beardtongue, Hartweig evening primrose, Mexican hat, chocolate flower, coreopsis, blanket flower, anthemis; buds on butterfly weed, black-eyed Susan and fernleaf yarrow.

Bedding plants: Sweet alyssum, pansy, snapdragon, moss rose, impatiens; buds on nicotiana; peppers still struggling with the heat.

Inside: Zonal geranium, aptenia, asparagus fern.

Animal sightings: Small and large hummingbirds, house finches and other small birds, gecko, bees on catmint, cabbage butterfly, small flying insects, harvester and small black ants; hear crickets.

Weather: Air smelled of burning chemicals Monday from fires to the southwest; all week the Jemez grew slowing indistinct at sundown, sometimes disappearing altogether while the sun turned red as it entered the layer of dust and ash; some mornings temperatures fell into the 40's and others they didn’t go below 60; last rain 5/19/11; 15:55 hours of daylight today.

Weekly update: The biggest milkweed I’ve ever seen is blooming above the village ditch.

When I get on the bank, last year’s grey, furrowed pods are as high as my nose; when I stand on the road side, they’re above my head.

This year’s flowers reach my biceps. Fuzzy leaves, 7" long and 3 1/2" wide at their base, cuddle 3" balls dotted with pale pink stars. The supporting stems are about 3/8" thick.

This showy milkweed’s larger than any in the parent colony a mile away to the southeast where plants grow about two feet in a ditch bottom and along its inner banks. The difference is that water flows through the one ditch more often than it does the other. Even though this milkweed species ranges west from the great plains, it still needs water.

We’re outside any path used by migrating monarch butterflies, so this member of the milkweed family has been free to respond to the arid environment. Leaves and stems of Asclepias speciosa contains much less latex than those of the common milkweed, Asclepias syriaca, or the broadleafed Asclepias latifolia found on the edge of a monarch path in west Texas. However, they contain more than is found in the horsetail variety, Asclepias subverticillata, used by the Zuñi to the west.

While the absence of monarchs has meant a need to expend less energy to defend against predators, it has also meant the plant has to attract some other insect to fertilize its flowers. Large blossoms and great quantities of nectar are two obvious devices of allurement.

Their green centers contain consolidated reproduction units that snare the legs of unwary insects. As they free themselves, they dislodge packets of pollen which they shake off or drop when they approach the next flower.

The bee I saw land on one of the flowers was extremely cautious, approaching the cluster from the base and attacking a flower from one of its bottom points.

Unfortunately for the milkweed, the insect is likely to go to the next available flower on the plant instead of flying to another plant and a plant can’t accept its own pollen. Matthew Finer and Martin Morgan found plants they deliberately pollinated produced more pods than those in the wild where insects alone did the fertilization.

What’s surprising is that the plants they hand pollinated, but left available to insects also produced fewer pods than the ones they pollinated but covered so insects couldn’t reach them.

Susan Stone Bookman thinks the reason is showy milkweed plants have a finite ability to feed themselves and so are forced to kill off more than 95% of the flowers and potential pods. Mature pods contain two to seven times the amount of nitrogen, potassium and phosphorus as young ovaries.

From this, it’s easy to see that flowers that are pollinated first would be most likely to survive than those visited later, and that afternoon fertilizations, when the plant is more stressed, would be less successful. What’s not self-evident is that, if enough time passes, Bookman found another flower in a cluster can be successfully pollinated.

While very few pods survive to tower above the living mass of grey-green leaves, the dark flat seeds they produce are extremely viable. In one test, 95% emerged the first year, most in May, and the rest before the end of July. They can even survive some time in water and still germinate.

Young seedlings concentrate on developing what will become long taproots which allow them to survive the early summer droughts that precede the monsoons. As a result, they can be choked by surrounding vegetation before their stems rise into the sun.

The milkweeds in the village landed near a fence covered by Virginia creeper. The warm weather perennials don’t put out their leaves until after the vine, and so must shove their way through their competitors every year.

Although most are single plants rising from a crown, some specimens apparently can produce additional plants from their roots when conditions require. However, the presence of nearby clones increases a plant’s problem with endogamous pollen.

Botanists raised in a world where they’re told market forces rule supreme like to do cost-benefit analysis or energy efficiency assays for plants, hoping in the process they are finding the key to evolution. Perhaps I’m a hopeless romantic when I think the lives of milkweed are more than a series of sacrificial tradeoffs made to survive an irrational climate, that their moments of grandeur are more than feeding opportunities for bees.

I know they don’t exist for my aesthetic pleasure, that the slim chance of my noticing them as I drive by is of no concern to nature. Still, such events occur and just might also aid their survival. After all the ditch holding the parent colony is cleared every year, and the milkweeds persist.

Notes:Agrawal, Anurag A., Marc J. Lajeunesse and Mark Fishbein. “Evolution of Latex and its Constituent Defensive Chemistry in Milkweeds (Asclepias): a Test of Phylogenetic Escalation,” Entomologia Experimentalis et Applicata 128:126–38:2008; the latex levels they found were: subverticillata: .277, speciosa: .819, syriaca: 1.540, latifolia: 5.925; all by syriaca occur in northern New Mexico.

Bookman, Susan Stone. “Costs and Benefits of Flower Abscission and Fruit Abortion in Asclepias speciosa,” Ecology 64:264–273:1983.

_____. “Effects of Pollination Timing on Fruiting in Asclepias speciosa Torr. (Asclepiadaceae),” American Journal of Botany 70:897-905:1983.

Conrad, Jim. “Milkweed Flowers,” Backyard Nature website, has a clear description of milkweed flowers with good pictures.

Finer, Matthew S. and Martin T. Morgan. “Effects of Natural Rates of Geitonogamy on Fruit Set in Asclepias speciosa (Apocynaceae): Evidence Favoring the Plant's Dilemma,” American Journal of Botany 90:1746-1750:2003.

Ulev, Elena D. “Asclepias speciosa,” 2005, in United States Forest Service, Fire Effects Information System on-line database; summarizes research of others, including W. S. Chepil’s “Germination of Seeds. I. Longevity, Periodicity of Germination, and Vitality of Seeds in Cultivated Soil,” Scientific Agriculture 26: 307-346:1946.

Photograph: Showy milkweed growing with Virginia creeper outside a 4' fence atop a village ditch bank, 5 June 2011; last year’s pods rise on the brown stalks in back; a flower opened wide at the bottom left shows the green center.

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