Cholla Fields of New Mexico

On my trip down the Dry Cimarron River, across the High Plains, and then on to the Cimarron proper, I often saw vegetation brand new to me but apparently common in New Mexico. From a distance I thought it was grassland with heavy shrub cover, maybe mesquite. But soon the distinctive form of the “shrubs” was obvious: thickish stems, awkward branching, no leaves. These were cacti.

Dry Cimarron valley, land of cacti and clastic plugs (mid photo).

The cactus was unfamiliar, but easy to identify: Cylindropuntia imbricata, tree cholla. It’s large, three to seven feet tall, even 10 or 15 under favorable conditions. Often there’s a short “trunk” that soon branches. Spines are sparse, revealing green jointed stems. The yellow fruits stay on the plants through the off season. The most helpful features are the tubercles—bumps on the stems bearing specialized buds (areoles) that produce spines (more here). Cactus tubercles are usually described as “small rounded projections” but those of the tree cholla are large and elongate. The sparse spines make them easy to spot.

Yellow fruit from previous year still on plants in early May.

Stems are sometimes reddish in winter.

Prickly pear cactus (Opuntia polyacantha) has “small rounded” tubercles.

Distinctive elongate tubercles of the tree cholla.

Being a veg ecologist of the American West, I was suspicious of these cholla fields. Heavy shrub cover in grassland often indicates over-grazing. Livestock almost always prefer grass to shrubs, giving the shrubs a competitive advantage that can lead to dominance. How about tree chollas? Surely no cow or sheep would eat one if grass were available.

Grassland thick with tree chollas, Dry Cimarron Valley (with ghosts of travelers past).

Tree cholla grassland on the High Plains north of Clayton.

Tree chollas, just west of Cimarron.

Back at home, I looked for tree cholla vegetation types in the US National Vegetation Classification. I found a good match: Opuntia imbricata Ruderal Shrubland (Opuntia is a synonym for Cylindropuntia). My suspicions were confirmed:

“This anthropogenic (semi-natural) shrubland results from overgrazing of native grasslands. It occurs particularly in slightly moister settings along broad swales. Infestation of Opuntia imbricata [synonym for Cylindropuntia imbricata] is variable, and cover of Opuntia in this type ranges from 25% to nearly 100%. Grass cover and composition is highly variable, depending on site and grazing regime and history. This broadly defined community grades to grassland (often with some Opuntia cover) or to other grazing-induced shrubland communities, such as those dominated by Prosopis, Acacia, and/or Mimosa” [shrubs in the pea family] (NatureServe Explorer).

Now the inevitable counter-questions: What about bison (buffalo)? There was a time not all that long ago when bison numbering in the millions roamed the American West, including New Mexico. What did these grasslands look like then? How common was tree cholla? Did bison eat it as readily as grass? The answer: we don’t know and probably never will (add these to life’s persistent questions).

But these questions are irrelevant where tree cholla has been introduced. It’s now widely naturalized—in eastern and southern Europe, northern and southern Africa, southern South America, and eastern Australia, often to the detriment of grasslands. For example, in Queensland, it threatens native semi-arid grasslands, and has been listed as a priority environmental weed (source).

Ironically, while land managers try to find a way to eradicate tree cholla (e.g., fire, chaining, chemicals), gardeners are encouraging it. “C. imbricata is one of the best chollas for desert landscaping. … It is an attractive plant in desert gardens, and cultivation is quite easy” [for the same reason it’s so hard to eradicate in pastures]. “All you have to do is plant one of the ten-twelve-inch stems in the ground. Water it after it has a chance to put out roots, in a few weeks.” Saguaroland Bulletin v.30:no.1-10 (1976)

Summer flowers (NPS).

Tree cholla is not restricted to desert gardens. It has long been grown in Europe, though not without challenges:

“It is the commonest member of the group to which it belongs in European gardens, and was first introduced to cultivation in the earlier years of the nineteenth century. In spite of this, however, it is a plant whose flowers, which are very attractive but which will only expand under the influence of direct sunshine and unfortunately do not last long, are not often seen in the United Kingdom. Sir Edmund Loder informs us that his example at Leonardslee has but seldom flowered; when it did so in 1908 this happened during a time of very hot, sunny weather, and individual flowers only remained fully open during one afternoon, from about midday till sunset.” Curtis’s Botanical Magazine v. 135; 1909

Curtis's Botanical Magazine, 1909 (courtesy Biodiversity Heritage Library).

Tree unchanged, but something of interest as always

Another month has passed and I feel it. Perhaps this is an age-thing: already another month! so much to do yet!! etc. But the boxelder I’m following seems oblivious to the passage of time. It stands unchanged month-to-month, and barely moves even when the wind is howling, apparently protected there in its corner.

But its neighborhood changes. Most recently, someone parked a pickup equipped with a snowplow nearby. We’ve had so little snow this winter, maybe that’s why it was left there—nothing to do. Now it’s gathering tumbleweeds.

Russian thistle, Salsola kali, in center. Seed heads upper right are from an unknown plant.

If you park on the west side of a building on the west edge of town, tumbleweeds soon accumulate.

I recently posted about tumbleweeds as urban plants at my other blog, the one I (and readers) largely ignore. It was about the tumbleweed world we live in here on the west side of Laramie. This was my contribution to a neat monthly meme hosted by Lucy of Loose and Leafy in Halifax. If you enjoy tree-following, you might also find street plants of interest. More here.

When I looked more closely, I discovered that what I thought was a large tumbleweed was actually a rooted plant that the driver parked adjacent to, enhancing the tumbleweed trap. Its seed heads are visible upper right in the closeup photo above.

Part tumbleweed, mostly something else.

Tumbleweed trap with unknown plant behind, field assistant in foreground.

I didn’t recognize the plant, so I brought some heads home to examine. I knew it was a composite (family Asteraceae), and figured it probably was a “weed.” So I searched through my copy of Weeds of the West. As always when I browse this book, I was soon disgusted by how many perfectly fine native plants are included as “weeds.” But the photos and descriptions are good (it's now free online, use link above).

Tools of the trade.

My specimen was poor—old dried wind-beaten seed heads, no leaves. But it looked a lot like what we call Russian knapweed, which I thought was Centaurea repens. But of course plant taxonomy doesn’t stand still. In 1995, Centaurea repens became Acroptilon repens. In 2006, it was renamed again: Rhaponticum repens. Both newer names are currently used in various official lists (e.g. here and here). Frequent taxonomic revision frustrates some of us who were told that scientific (Latin) names were worth learning because they avoid the ambiguity and multiplicity of common names … yeah, right :(  But I’ve been assured several times that plant nomenclature is beginning to stabilize, so I try to be patient.

I do like the alternative common name for Russian knapweed and several other knapweeds: HARDHEADS! After a bit of googling, I found this explanation:

“If you pinch off an old flower head in the autumn, pull off any loose seed heads, there is a very hard kernel. If you then carefully split this there is a good chance that there will be a small grub inside. Goldfinches can often be found feeding on these grubs.”

I found no hard kernels but then I didn’t have much material. Also, the grubs might be specific to Centaurea nigra, which is also called hardheads. Fortunately for me, the repens hardheads (I can’t resist this name :)) is a perennial. So if my id is correct, I should be able to follow it as well as the boxelder. I say “fortunately for me” because most people who know Russian knapweed hate it. It's considered a horrible invasive in North America, and is designated noxious in 46 of the 50 US states. But as with the boxelder, I’m hoping no one notices hardheads here in its urban hideaway.

Thanks to Pat of The Squirrelbasket for hosting our monthly tree-following gatherings. For the latest news from followers far and wide, read here.

Beauty amid Destruction

Year #25, dog #3.

For 25 years we’ve walked the dirt road to the river—a morning ritual. It runs along railroad tracks that serviced the old packing sheds. For the last two years, the tracks have been disappearing, bit by bit (I suspect this is someone’s side job). Now the rails are gone, and ties lie in heaps. Much of the thistle–tumbleweed vegetation has been bulldozed away.

With bare soil, more sunshine (less thistle), and lots of late spring and summer moisture, the old track bed has become a garden of pioneering plants. In our yards we call them “weeds” but here they are beauties—high-impact beauties in fact, given the surrounding destruction and decay.

Evening primroses are well-represented. True to their name, the flowers open in the evening, stay open for our morning walks, and then close in the heat of midday. Most of our species are white-flowered and moth-pollinated, hence their nocturnal habits. But there are a few yellow-flowered ones too.

I found one hairy evening primrose, Oenothera villosa. It's a common colonizer of open areas along the river, about a quarter of a mile away, and I bet there will be more here soon. The yellow flowers appear to open in the evening and close in the heat of midday, so who are its pollinators if not moths? Or do moths notice yellow flowers? So much to learn.

Nuttall’s evening primrose, O. nuttallii, is common along the dirt road. Now it's invading the newly-bare thistle-free soil. It grows to be almost shrub-like, but being a true forb, it dies back each year. The flowers are about 5 cm across, showy by local standards.

Crownleaf evening primrose, O. coronopifolia, is small perennial herb with flowers about 2.5 cm across. The lobed leaves are said to be suggestive of crowns. UPDATE: For alternative explanations, see Pat the Plant's Comment and my Reply below.

Crown-like leaves?

Against the wall stood another flower of the night—white campion, Silene latifolia. Wikipedia notes “it is also named the Grave Flower or Flower of the Dead in parts of England as they are seen often growing on gravesites and around tombstones.” White campion is dioecious, with male and female flowers on separate plants. This one's a guy—just stamens in the flowers.

Foxtail barley is common in the Laramie Basin, often on slightly saline soils. The bulldozer brought sun into its life, and now it’s flourishing, helped by runoff from the buildling.

Finally, the surprises. Two are plants of moist habitat—surviving here due to runoff. Based on size, they must have been here for awhile. I guess I didn’t notice them behind the tumbleweeds.

Narrowleaf cottonwood, Populus angustifolia. Its parents probably are among the trees along the river.

Meadow foxtail, Alopecurus arundinaceaus, a non-native that usually grows in wet meadows.

The biggest surprise was fireweed, Chamerion angustifolium (other names include rosebay willowherb and blooming sally). It’s a famous fire-follower, growing luxuriously where fire has burned off both the tree canopy and ground cover, exposing bare dirt in full sunshine. But it also thrives on other kinds of disturbed sites.

I know fireweed well, from montane habitats. Surely if it were growing next to the packing sheds all these years I would have noticed it. Did it appear this year because of a fortuitous combination of factors—moisture, shade-removal, bare ground? Had its seeds lain dormant for years? Or did they blow in recently? Or did these shoots sprout from roots or rhizomes? (or did I just overlook it?!)

I found conflicting reports—surprising for such a widespread and well-studied plant. According to the thorough and well-documented USDA Forest Service FEIS Database, fireweed does not produce long-term seed banks. However, Wikipedia says seeds remain viable in soil for many years. In any case, fireweed produces lots, and they germinate readily in bare soil over a wide range of temperatures. Even so, vegetative reproduction is more common. Following disturbance, especially if the underground rhizomes are cut, shoots sprout and grow rapidly, sometimes reaching nine feet in height!

Purple and green, my favorite color combination.

The long narrow pods are loaded with tiny seeds ... as I found out later.

I collected flowering stems from some of these beauties, and took them home for closer examination … and more surprises!

To be continued …

See the bee?

Can you find the happy bee, feasting on nectar? (click to view ... maybe)

My header photo is changing soon has changed, so this is a good time to pay tribute to the Rocky Mountain bee-plant, featured during my first year of blogging (old header is at end of post).  Its Latin name is Cleome serrulata, and the common names are many:  Rocky Mountain beeweed, spider-flower, stinking-clover, stinkweed, Navajo spinach and others.  I prefer bee-plant because it clearly is one.  Every summer when the ones in the backyard bloom, they fill with bees.  The buzzing is quite audible.  When I walk through the bee-plant forest, few bees notice.  They keep foraging intently, focussed entirely on nectar.

Given the inadequacy of the display on my point-and-shoot in full sun, all I can do is point and hope that I’ve caught a bee or two.  Fortunately there are so many bees in the bee-plants that my chances of getting at least one are good.

Bee on bee-plant.

Try an easier one:

Here's one of the bees (center left in photo above):

and another -- a bee butt shot:

Rocky Mountain bee-plants are robust tap-rooted annuals that can grow to four feet in height.  The leaves are compound, made up of three leaflets (left).  As some of its common names suggest, the plants are malodorous -- described as horrible, foul, skunky and like over-cooked spinach.  I don’t find the odor that offensive; in any case, it isn’t terribly strong.  It disappears with cooking, and bee-plants were collected and eaten by various American Indian tribes.  "Navajo spinach" is still used by the Navajo, both for food (so I've read, though it requires lots of boiling) and as a source of black dye for pottery.

Pink-and-green is the theme: green leaves and pink flowers, with pink filaments topped by green anthers!

Given enough space and a little rain every now and then, Rocky Mountain bee-plants branch widely, and produce many clusters of magenta-to-pink or sometimes white flowers.  The flowering period is long; my stand of bee-plants blooms almost until the end of the growing season.  Flowers are similar to those of the closely-related Mustard Family, with four sepals, four petals, six stamens and a single pistil.  The stamens are particularly lovely, with long pink filaments and green anthers.  Inside the flower, at the base of the ovary, is a gland that produces abundant nectar.  This is why bees love bee-plants.

Pendant pods develop even as new flowers continue to be produced; each pod contains about 20 seeds.  A healthy bee-plant will yield on the order of 25,000 viable seeds!  Doves are famous for their fondness for bee-plant seeds, but it is sparrows and finches that consume most of the ones in my yard.  They eat them right off the plants -- these large annuals are robust enough for small birds to perch on the branches.

Rocky Mountain bee-plant was formally described by Frederick T. Pursh in 1814, based on three specimens collected by the Lewis and Clark expedition in what is now South Dakota.  It is native to much of western North America and the Great Plains, and has become naturalized further east.

Cleome serrulata, from Pursh's 1814 treatise on the flora of North America.

A bee with a plan ...

The University of Wyoming and the Western Society of Weed Science have officially proclaimed Rocky Mountain bee-plant to be a weed, for the simple reason that livestock won’t eat it (Whitson 1991).  Never mind that it occupies disturbed sites, does not persist as vegetation becomes established, does not invade intact grasslands, and provides high-quality habitat for a wide-range of pollinators.  A land manager that turns to this “definitive work” on weedy plants of the western US will treat Rocky Mountain bee-plant as a weed.  Sad.

A little research would have prevented this error.  Our two species of Cleome (the other is C. lutea, yellow bee-plant or spiderflower) are known to be excellent resources for pollinators.  The diversity of insects that forage on bee-plants is impressive.  Cane (2008) reported that 162 native bee species were found on bee-plants (both species) in Grand Staircase - Escalante National Monument in southern Utah.  Most were generalists that visit a wide range of native and agricultural plant species.  Two important managed agricultural pollinators also utilize bee-plants when available -- alfalfa leaf-cutting bees and honey bees.

... oh boy! treats ahead!!

Bee-plants also are recognized for their ability to colonize disturbed sites, and have been recommended for reclamation seed mixes as well as for rehabilitation of western rangelands (Cane 2008).  The plants grow well with very little care or water, and produce large quantities of viable nutritious seed.

Last year, Ralph demolished a flower bed in the interest of a new sewer line.

This year, the bee-plants are back, all on their own.

Information Sources

Cane, J.H.  2008.  Breeding biologies, seed production and species-rich bee guilds of Cleome lutea and Cleome serrulata (Cleomaceae).  Plant Species Biology 23: 152-158.

Pursh, F.T.  1814.  Flora Americae Septentrionalis or, A systematic arrangement and description of the plants of North America.  Vol. 2.  London:  White, Cochrance, and co.  Available at: http://www.botanicus.org/item/31753000141777

Tucker and Vanderpool moved the Rocky Mountain bee-plant to the genus Peritoma in the Flora of North America.  See http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10199 for more exciting details :-j

The USDA Forest Service featured the Rocky Mountain bee-plant as Plant of the Week.

Whitson, T.D. 1991.  Weeds of the west: Western Society of Weed Science in cooperation with the Western United States Land Grant Universities Cooperative Extension Services.  Laramie:  University of Wyoming.