Mentzelias

Blazing stars (Mentzelia species) can be tricky to identify. There are over 70 species, some not well-described in the literature, at least not in the readily-available literature. Mentzelia involucrata is easy enough, though, since it’s rather showy and common.

Even so, I second-guessed myself with some of the pictures. There’s a similar-looking, M. hirsutissima, which I thought I’d seen. But it’s a rare species, and you know what they say about extraordinary claims. I was able to eliminate that possibility once I read that only M. involucrata has floral bracts that are white with green edges.

M. involucrata is an annual plant growing to a little over a foot tall in both the Sonoran and Mojave deserts.

There were a few other small, yellow flowers that weren’t so easy, though. I could place them in the Loasaceae by observing the leaves, the flower shape, and the number of petals and stamens. Plants in this family tend to be low-growing, with thick, sometimes hairy, lobed or dentate leaves; the flowers have five radially symmetrical petals and many stamens.

Once I figured out Loasaceae, getting to Mentzelia was easy, since it’s the only genus represented in the area (according to the comprehensive San Diego County Native Plants). Then it was over to the excellent CalFlora website, which showed 18 Mentzelia species in the Anza-Borrego area. A close look at the location records and habitat information allowed me to eliminate all but four species as possibilities. Detailed descriptions at SEINet led me to eliminate two more, with some uncertainty, leaving two likely candidates: M. affinis (yellowcomet, yellow blazing star) or M. albicaulis (small flowered blazing star, whitestem blazing star). I just don’t have enough of the right details in the pictures to be certain, but after reading various descriptions I’m leaning toward identifying this one as M. affinis.

Mojave, Mohave, Mohavea

Do you know the web comic xkcd? I was reminded of it the other night. While getting ready for bed I glanced over Steve’s shoulder at his iPad. “Hey, you’re reading my blog!” I beamed. “Yep,” says he. “I think you made a mistake.”

So I immediately went back to the computer and corrected every instance where I’d typed “Mohave” instead of “Mojave”. I hate making mistakes like that. I work hard not to make mistakes like that. Why did I make a mistake like that?

I blame this flower: Mohavea confertiflora. Ever since identifying it and adding it to my spreadsheet, I’ve been mixing up the words and typing them wrong.

Ghost flower is an annual that grows to about ten inches tall, bearing single flowers in the leaf axils, and is easily identified by the red spots inside the petals. It can be found on washes and gravelly slopes in both the Sonoran and Mojave desserts. Its cousin Mohavea breviflora is found in the Mojave and Great Basin deserts.

In other news of genera starting with M, I found several species of Mentzelia. More on them next time.

In case you’re wondering, the lead photo shows ghost flower, rock daisy, gold poppy, and two different species of phacelia.

above, xkcd “Duty Calls”

[I proofread this post a coupla dozen times.]

Carderock Area Report

As of March 24, there’s still not much blooming yet. Harbinger of spring is in full bloom, or even slightly past, and round-lobed hepatica (pictured) and lyre-leaved rock cress seem to be at their peaks. Spring beauties are blooming but not en masse. Other native plants seen just starting to open:

  • Virginia bluebells
  • leatherwood
  • cut-leaved toothwort
  • star chickweed
  • wild blue phlox
  • common blue violet
  • spicebush

Golden ragwort is starting, too, well downstream of the Carderock area. Dutchman’s breeches and trout lily foliage is now visible through the leaf litter.

Until the show really gets going I’ll keep posting about Anza-Borrego.

More Cacti

Ferocactus cylindraceus

California barrel cactus is native to the Sonoran and Mojave deserts, growing in various rocky and gravelly habitats. Younger specimens have redder spines and a more rounded stem, while older specimens have grayish spines and a cylindrical stem that typically grows to about five feet tall, sometimes taller.

Weird fact: this species is known to grow somewhat faster on its shaded side, so that older plants lean toward the southwest, which explains the common names “compass cactus” and “compass barrel”.

Although the IUCN* Red List categorizes California barrel cactus under “least concern”, some sources claim that the species is vulnerable to poaching by collectors.

I found this and many more specimens of California barrel cactus mostly in the flat plains near Borrego Springs, rather than on the slopes of canyons.

 

Mammillaria dioica

Fishhook cactus, aka strawberry cactus, has a small range that includes San Diego, Riverside, and San Bernardino counties as well as Baja California and Sonora states in Mexico; some sources also show it present in Imperial County. But it is not a rare species; IUCN calls it “locally abundant” and it’s on the Red List as “least concern”. Nonetheless, I found only two specimens, near Hellhole Canyon. Several authorities agree that there are three subspecies of M. dioica, though IUCN notes “this is a taxonomically complex species”. I don’t have enough information to say which subspecies this might be.

Fishhook cactus grows on dry slopes. Authorities state its size as anything from six inches to one foot tall; this specimen was closer to one foot.

This is one of the few cactus species that doesn’t always bear perfect flowers. Some specimens do, while others bear flowers with functional “female” parts and sterile anthers.

Note the other cactus in the lower left of the last photo. With not much information to go on I’ve tentatively identified it as Echinocereus engelmannii (hedgehog cactus). If you know it, please leave a comment!

 

 

*the International Union for Conservation of Nature; the Red List is a global accounting of species’ conservation status.

What Makes it a Cactus?


And, back to wildflowers.

The pictures in yesterday’s post were of beavertail cactus, Opuntia basilaris, one of the earliest blooming cacti in the Anza-Borrego region. It grows in many different habitats of the Sonoran and Mojave deserts, and is easily identified as an Opuntia by the characteristic flat pads that appear to be spineless. It’s further identified as O. basilaris by the pink flowers (other species’ flowers are yellow). About those spineless pads: they aren’t spineless. The spines are just very small. They’re also barbed. Since this is botany, there has be be a word for them. They’re called glochids.

Beavertail has a cousin here in the Maryland piedmont: eastern prickly pear (Opuntia humifusa).

Cactus is one of those botanical terms that’s often mis-used colloquially, referring to any succulent plant. Succulent just means that the plant has organs that store water, while a cactus is any plant that is a member of the cactus family, Cactaceae.  There are many succulent plant species in the world, but only some of them are cacti.

So what makes it a cactus?

A number of things, taken in combination. First, cacti have spines, which are modified leaves. Spines are not the same as thorns, which are modified stems, or prickles, which arise from epidermal tissue.

Since (with very few exceptions) cacti don’t have true leaves, photosynthesis happens via the stems, which are succulent and often cylindrical, globular, or pad-shaped.

the things that look like dots on the stem are the aureoles; zoom way in to see some glochids in the upper ones

The spines arise from structures called aureoles, which are a defining feature of cacti; no other plants have them. Aureoles also give rise to new stems (on branching species) and to flowers.

Cactus flowers are showy and usually radially symmetrical, with numerous petals and sepals (which can’t be distinguished from one another). They are also usually bisexual, with numerous stamens and a single pistil with an inferior ovary (which means that it is located below the petals and sepals).

With the exception of a single species, all cacti are native to the New World.

Weird cactus fact: there are cactus species native to the the rainforests of Central and South America. Yes, cacti grow in the rainforest, as epiphytes on trees where there’s little organic detritus to form soil and water doesn’t collect, a situation like an extremely localized arid-yet-humid microclimate. Isn’t that nifty?! The common household plant Christmas cactus (Schlumbergera species) is one example.

next time: more cacti

interesting reading
CactiGuide.com
Spines, Photosynthetic Tricks, and Other Marvels of Cacti Evolution