flowers

Houndstongue is a noxious, poisonous weed with nasty seeds and pretty flowers

Anonymous — Tue, 30 Apr 2024 19:40:20 +0000

Houndstongue is a noxious, poisonous weed with nasty seeds and pretty flowers Anonymous (not verified) Tue, 04/30/2024 - 13:40

Professor Emeritus takes a closer look at beautiful weeds with a lethal potential to kill livestock, and even, humans

After spending several hours stalking and photographing butterflies on Flagstaff Mountain west of Boulder, I returned home and spent about 10 minutes removing burs from my jeans and wool socks. I was annoyed, for if I only knew what plant bore those burs, I could give it a wide berth.

A year later, when processing my photo of a western tailed-blue (Cupido amyntula) on a cluster of flowers, I found the answer in the photograph. In the foreground were the flowers of houndstongue (Cynoglossum officinale). In the background were the maturing burs or seeds that were so annoying.

Houndstongue takes its common name from the similarity between its leaves and the tongue of a panting dog. Each leaf contains veins or groves that spread down to the distal or outer part of each leaf resembling a green tongue.

Houndstongue is native to the United Kingdom, northern Europe and northern Asia. It was thought to have been introduced to Canada in a contaminated shipment of seed before 1859. No one noticed the contaminated shipment, but specimens of houndstongue were collected in 1859 and deposited in a herbarium in Ontario. It was first reported in the United States in Oregon in 1893 and Montana in 1900. Today, houndstongues are in most of the 48 contiguous states and are listed as noxious weeds in seven western states, including Colorado.

A fertilized flower produces a fruit that is composed of four nutlets, which are thick-walled shells covered with barbed prickles and each containing one seed. (For simplicity, seeds, burs and nutlets will be called seeds). The seeds in the accompanying photo have a dense coat of straight green prickles. As the seeds dry, the prickles become barbed hooks, enhancing their ability to cling to animal hair. The seeds are dispersed by many species of mammalian wildlife, as well as cows, sheep, goats, horses and dogs.

The seeds—which hitchhike on sheep, cows, horses, dogs and hikers—are thoroughly annoying. Sheep wool can be so densely packed with nutlets that the fleece loses value. In the United Kingdom, people who take their retrievers for a walk or to retrieve ducks may spend an hour removing seeds from the dog's pelt and from wool hunting jackets. In the western United States, the seeds slow the marketing of cows, for they must be removed before cattle can be sold.

The seeds are annoying, but their plant defenses cause even greater problems. Like most species of plants, houndstongue has defenses that have evolved to discourage herbivores. Although it has no thorns, it has chemical defenses that are ingested by herbivores that eat its flowers, seeds, leaves and stems. It synthesizes four different pyrrolizidine alkaloids (PAs), which the liver converts to pyrrolic metabolites that cause tumors, damage nuclear DNA and halt protein synthesis in liver cells. So, PAs poison the liver and turn off the cell replication that may have replaced damaged liver cells.

A western tailed-blue butterfly on houndstongue flowers with seeds in the background. Image by Jeff Mitton.

PAs have killed humans, cows, horses, farmed deer, pigs, sheep, goats, poultry and quail. Horses are most susceptible, and sheep and goats are remarkably less susceptible with a tolerance to lethal doses 20 times higher than most animals. Most species of wildlife are not killed, but they learn not to graze on houndstongue. Because wildlife learns to avoid houndstongue, it has a competitive edge over the healthy sources of food both wildlife and cattle eat. In some places, this competitive edge allows houndstongue to become the dominant species, which greatly degrades the value of pastures for grazing.

PAs are synthesized by about 5% of all flowering plants and occur in 20 plant families. More than 600 forms of PAs have been described from the approximately 6,000 species that have been examined. None of these compounds are necessary for plant development, growth or reproduction—their functions are limited to plant defense against herbivores. The efficacy of these compounds can be seen in the speed of their invasion of Canada and the 48 contiguous states, despite efforts to eradicate or control them.

While clinging seeds and PAs give houndstongue a bad reputation, I must say that they have pretty flowers. Five petals fuse to form funnel-shaped flowers that appear from leaf axils and the tips of branches. The flowers are not one hue, but each flower has a combination of reds, blues and purples, so the flowers on one plant exhibit a range of colors. I will continue to enjoy the flowers, but I will approach only tentatively, avoiding seeds, and I certainly will not try the leaves in a salad.

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Top of page: Houndstongue up close look fragile, but are more robust than meets the eye. Images by Ben Legler.

Professor Emeritus takes a closer look at beautiful weeds with a lethal potential to kill livestock, and even, humans.

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Twinpods have many species adapted to harsh soils

Anonymous — Thu, 18 Jan 2024 19:18:38 +0000

Twinpods have many species adapted to harsh soils Anonymous (not verified) Thu, 01/18/2024 - 12:18

Jeff Mitton

Of the genus Physaria, pretty wildflowers, 24 species grow in Colorado. Ten of 24 species are endemic to Colorado, meaning they live nowhere else

As I turned over in my sleeping bag, I noticed that the stars had faded and the sky had a bright red glow. I grabbed the camera, caught the sunrise, then looked around to see what was stirring.

A shaft of sunlight making its way through pinyon pines and junipers isolated a double bladderpod, Physaria acutifolia, and highlighted its pink seed pods. As the seed pods mature, their colors change, starting with green but changing to yellow, then pink, then purple, and finally drying to grey or white. This species is one of the earliest plants to flower on the Colorado Plateau and is the most common Physaria in the region. P. acutifolia is relatively widespread, with populations in Colorado, Utah, Arizona, New Mexico and Wyoming, and just a few populations in Idaho and Montana.

Double bladderpods flowering. Image by Jeff Mitton.

Physaria is Greek for bladder, and acutifolia refers to leaves with sharp edges. Common names for species in this genus are twinpod or bladderpod, referring to the forms of the didymous seed pods, shaped like two balloons pressed together. In medical jargon, didymous refers to testicles, providing insight into the forms of two species, P. didymocarpa and P. scrotoformis.

Physaria is a mustard, one genus in the Family Brassicaceae, which has a total of 374 genera. But Physaria can be distinguished from the other 373 genera by the form of its trichomes, minute appendages projecting from the epidermal cells of leaves and shoots.

The common form in the mustards is dendritic, meaning they look like trees, with just a few branches. In sharp contrast, all of the Physaria have stellate or star-shaped trichomes. Each epidermal cell has one trichome, but it branches profusely, and the branches grow just above and parallel to the epidermis.

Al Schneider, in SouthwestColoradoWildflowers.com, describes the trichomes in Physaria this way "the star-burst pattern of the hairs make the leaf appear to be covered by thousands of minute sea anemones." Trichomes have many functions, but Physaria's stellate trichomes are thought to protect leaves from the desiccation and bright sunlight of desert and alpine environments.

Abigail Mazie and David Baum explored the evolution of stellate trichomes in Physaria with analyses of BLT, a gene that appears to influence trichome branching in mustards. Analyses of DNA sequence evolution found evidence of strong natural selection on BLT in Physaria. They could even determine that selection was strong in the species that first expressed stellate trichomes, but they also noted that selection continues today in Physaria species most recently evolved. Stellate trichomes are a very convenient character to identify species of the genus Physaria, and in addition, the trichomes appear to have continuing importance in adapting species to their environments.

Currently, 106 Physaria species have been described, and 24 species are in Colorado. What is striking is how many are endemic, meaning they live nowhere else. Of the 24 species in Colorado, ten are endemic, and in contrast to the widespread P. acutifolia, many species have tiny geographic ranges. A few examples follow.

Bell's twinpod, P. bellii, is adapted to Niobrara and Pierre shales, although it is found on a few granite substrates. Its entire distribution is between Fort Collins and Ken-Caryl Ranch Natural Area in Denver. Most of its populations are just dots on a map of Boulder County. P. bellii puts on a bright floral display against dark shale on the outcrops at the intersection of Colorado 36 and Neva Road.

Double bladderpod's seed capsules catch early sunlight. Image by Mitton.

The Piceance Basin, in northwestern Colorado, is known for oil, gas and oil shale, but it also contains the entire ranges for two species, both called Dudley Bluffs bladderpod, P. congesta and P. obcordata. Both occur only on the white shale outcrops of the Green River Formation. P. congesta has seven known populations, and P. obcordata has 10 populations.

West silver bladderpod, P. scrotiformis, is a Colorado endemic. Furthermore, one could also say that it is an endemic of the Weminuche Wilderness Area, where it grows on limestone foundations at high elevations.

Physaria alpina is endemic to high alpine areas in northeastern Gunnison Basin and the Mosquito Range in Colorado. Twelve populations are known, but only four were evaluated to have good or excellent viability and over 1,000 individuals. One report estimates that P. alpina occupies only 187 acres.

These examples of tiny distributions are just a sample of the total. But it is sufficient to convince me that species in the genus Physaria have a genetic predisposition to establish populations on sites described as barren, with demanding if not poisonous soils, and adapt to them so quickly that the adapted populations are reproductively isolated.

However, I was unable to find any phylogenetic studies that used DNA data to date the ages of these species. Perhaps they are very young, or perhaps, once adapted to their barren sites, the population lineages linger, with little competition from other species. This is a fascinating puzzle that can be solved with genetic data.

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Of the genus Physaria, pretty wildflowers, 24 species grow in Colorado. Ten of 24 species are endemic to Colorado, meaning they live nowhere else.