Photo of the Week – February 9, 2017

Snow-on-the-mountain (Euphorbia marginata) is a showy plant, but not because of its flowers.  In fact, the flowers are tiny and very simple.  It’s the leaves (and some bracts beneath the flowers) that make the plant outstanding in its field.


Snow-on-the-mountain (Euphorbia marginata)

Like other relatives in the spurge family, snow-on-the-mountain’s flowers have no petals or sepals.  The small round white things that look like petals beneath the anthers are actually bracts, and all the other white parts are leaves.  Most of the leaves of snow-on-the-mountain are green, but they become variegated toward the top of the plant.  The leaves closest to the flowers are often nearly or completely white.

More snow-on-the-mountain.

More snow-on-the-mountain, showing the rounded white bracts beneath the flowers, and the variegated green and white leaves below those.

The weird flower structures and variegated leaves are not the only unique features of snow-on-the-mountain.  Some of you with biology backgrounds know that plants are often divided by their photosynthesis strategy.  There are C4 plants (often casually referred to as “warm-season” plants) which are most efficient at photosynthesis during hot temperatures and drought conditions, and there are C3 plants (“cool-season” plants) which are more efficient during other kinds of conditions.  A few of you might even know that there is a third photosynthetic pathway called CAM, which is particularly effective in very arid conditions.  As it happens, snow-on-the-mountain and other Euphorbs actually use all three photosynthetic pathways – the only genus of plants for which that is true (as far as I know).  There, now you all have something to talk about at your next family gathering.

Snow-on-the-mountain is often maligned as a weed that needs to be controlled via herbicide or mowing.  In truth, while it is closely related to leafy spurge (Euphorbia esula), snow-on-the-mountain is an annual plant that is opportunistic but not invasive.  Cattle don’t like the taste of it, so it is often left ungrazed when everything else around it is nipped off near the ground.  Snow-on-the mountain can thrive in overgrazed pastures and other places where the vigor of dominant grasses is suppressed, but it competes poorly against those grasses when they’re allowed to grow again.

I appreciate periodically seeing snow-on-the-mountain in prairies because I know that if it was able to germinate and grow, other plants (including less “weedy” perennials) probably got the same opportunity.  Except around water tanks or other places where repeated cattle impacts or other factors keep grasses suppressed, snow-on-the-mountain doesn’t hang around very long.

A small beetle feeds on pollen, seemingly unaware of the camouflaged danger lurking nearby (crab spider).

A small beetle feeds on snow-on-the-mountain pollen, seemingly unaware of the camouflaged danger lurking nearby (crab spider).

As if the weird flowers, variegated leaves, and triple threat photosynthesis strategy weren’t enough to make you love this unique and beautiful plant, here’s one more cool fact.  Snow-on-the-mountain and other spurges produce white milky latex in their leaves and stems just like milkweed plants and rubber trees.  The latex isn’t sap, it’s made by a completely separate production system and doesn’t travel through the plant.  It’s a defense mechanism that is bad tasting and irritating to the skin of many animals (including humans with latex allergies).

Snow-on-the-mountain is a gorgeous native wildflower.  It used to be more commonly planted as an ornamental because of its beauty, but also because it is relatively free of pests and diseases (due in part to its toxic latex).  Unfortunately, because cattle don’t like to eat it and it can be abundant (and very conspicuous) in overgrazed areas of pastures, it has gotten an undeserved reputation as a nasty weed.  Snow-on-the-mountain doesn’t want to take over the world.  It just likes to grow in places where nothing else is growing anyway, and it gives way politely when the neighbors start getting pushy.

Does that sound like an invasive plant to you?  It sounds to me like a plant that needs a friend.  Let’s be friends with snow-on-the-mountain.  What do you say?

Ragwort – Prettier (and More Valuable) than its Name Might Suggest

One of my favorite spring flowers is prairie ragwort (Senecio plattensis, aka Packera plattensis).  Its bright yellow flowers add welcome color to prairies every May, especially when it appears in high numbers.  We always try to harvest as much seed from the species as we can when we’re doing prairie restoration projects – partly because it fills some important ecological roles, and partly because I just like it.

Prairie ragwort along one of the hiking trails at The Nature Conservancy's Platte River Prairies, Nebraska.

Prairie ragwort was blooming along our hiking trails last week.  The Nature Conservancy’s Platte River Prairies, Nebraska.

Ragwort is typically a biennial, so it germinates and forms a rosette (a few basal leaves) its first season, then blooms and dies the next year.  I’ve read that the rosettes can survive more than one year before blooming, but I’ve never watched closely enough to confirm that at our sites.  Regardless, it’s one of a suite of opportunistic plants that can take advantage of open space created by drought, fire, and/or grazing.  I have a soft spot in my heart for those species because their presence and abundance helps me read what’s happening in our prairies.  When I see lots of ragwort and other opportunistic species in our sites, it tells me that the vigor of dominant grasses has been suppressed (because of weather, management, or both).  Suppressing dominant grasses is a major focus of our management work because that suppression facilitates the establishment and spread of many other plant species, not all of which are “weedy”.  While a number of opportunistic species (ragweeds, annual grasses, and many others) can indicate grass suppression, ragwort is nice because it also happens to be attractive – and because it flowers at a time of year when few other showy plants are blooming.

An eastern-tailed blue butterfly on ragwort at the Helzer family prairie by Stockham, Nebraska.

This eastern-tailed blue butterfly was feeding on ragwort at the Helzer family prairie a couple weeks ago.  Near Stockham, Nebraska.

A sweat bee on ragwort at the Helzer family prairie.

A sweat bee on ragwort at the Helzer family prairie.

Prairie ragwort attracts a large number of pollinators, including bees, flies, moths, and butterflies.  It is an equal opportunity resource for pollinators because it doesn’t hide or restrict access to its pollen or nectar with funny shaped flowers that require long tongues or other specialized body parts.  Everything is right there – available to any insect that lands on it.  In years like this one, when ragwort appears in big numbers, it might be the most important species available to pollinators during its blooming period.

I enjoy watching the ebb and flow of ragwort populations in response to our management, but I also like to monitor its establishment and spread in our restored (reconstructed) prairies.  Although its seedhead is fluffy like a dandelion, and the individual seeds can travel long distances, most end up falling near the parent plant.  As a result, new populations tend to radiate outward from the initial colonizing individual, and the size of ragwort patches can be an indication of the age of a restored prairie.  However, that pattern falls apart when a prairie isn’t managed with frequent disturbances because the populations can quickly shrink during years when thatch and vigorous grasses prevent seed germination and establishment.

A common checkered skipper butterfly feeds on ragwort in one of our restored Platte River Prairies.

A common checkered skipper butterfly feeds on ragwort in one of our restored Platte River Prairies last week.  The short heights of the grasses surrounding the ragwort plants in this photo are a result of both drought and grazing last year.

Ragwort is certainly not a rare plant in Nebraska, or one that is of conservation concern.  The droughty nature of our state helps keep populations strong, as does the prevalance of grazing in many prairies.  However, I think it’s important not to judge the value of plants by whether or not they are rare.  Ragwort, along with hoary vervain (Verbena stricta), common and show milkweeds (Aclepias syriaca and A. speciosa), and many other “weedy” wildflower species serve as great indicators of ecological events, step up to fill holes in weakened plant communities, and are among the more important wildflowers for pollinators in our prairies.

What’s not to like?