Mojave milkweed (Asclepias nyctaginifolia) with the signature plant of the Mojave desert, the Joshua tree (Yucca brevifolia), growing in the background.

I love milkweeds for their interesting biology and their beautiful flowers that can rival orchids in complexity and diversity. I have only seen a few individual plants, three to be exact, of Mojave milkweed (Asclepias nyctaginifolia) on my property. The species name refers to the superficial similarity of the leaves to members of the four o-clock family, Nyctaginaceae. When in bloom, however, any foliar similarities evaporate like desert rains, since the plant is clearly a milkweed (Asclepiadaceae, now usually considered Apocynaceae) with the characteristic 5-lobed flowers with two ranks of floral parts arranged in spurs and petals.

The colors are subtly gorgeous on Mojave milkweed flowers. For me, it’s their shapely architecture that is so fascinating.

Like all milkweeds, the sap is white latex. The long-lived perennial roots dive deep into sandy soil, frequently near a wash channel, and are thickened and rather fleshy to help store water and support the plant’s growth in dry periods. Mojave milkweed is a short herbaceous perennial usually under a foot tall (30 cm) and it can remain dormant for more than a year if rainfall is inadequate to inspire activity. However virtually any warm-season rainfall between March and October will encourage them to pop forth. This plant first sprouted in the middle of August 2014, about 6 weeks ago, and the flowers are fully open now in late September. Look at the floral structure – sensuous.

If some of the flowers are successfully pollinated, several pods will develop. As with other milkweeds, the pods will split laterally along one side when ripe and release flat brownish seeds with a parachute of silky hairs attached to help them disperse on the wind.

Asclepias nyctaginifolia is not very common either. Plants tend to occur as widely spaced individuals rather than in groups, and how they can get pollinated at such long distances is somewhat of a mystery to me. I used to have three plants on my 40 acres as I said, and no others within a quarter mile or more. How do they reproduce? Clearly being very long-lived perennials (decades or more) aids their chances, but many years pods fail to set altogether. And another year passes without seed dispersal. Perhaps I should manually pollinate them like a giant bumblebee to help them out. Shall I wear black and yellow?

This A. nyctaginifolia is growing on the margins of a roadside bladed into the desert about 3/4 mile away from me. The road does not see very heavy traffic and as such the deep-rooted milkweed is able to withstand occasional scrapings by the road grader blade and still survive.

The Mojave milkweed spends most of its time dormant underground, and just as long as it has a couple of undisturbed months above ground to photosynthesize food, flower, and set seeds, this condition of surviving on the edge of a periodically graded roadside as seen above can continue indefinitely. It’s not ideal obviously, but tenable. The road it grows on was first bladed into the then-virgin desert in 1998, and I suspect that the milkweed well predated it. I highly doubt that some seedling germinated here after the road was installed, given their longevity and paucity of seed production or general abundance. I think this individual is simply surviving the road that overlays it now, simply because it doesn’t see that much vehicular traffic. Tough survivor!

Milkweeds are famous for being the larval host plant of the orange and black monarch butterfly (Danaus plexippus) We actually have relatively few monarchs here in the desert southwest, but the closely related, browner queen butterfly (Danaus gilippus) is quite common albeit nowhere near as well known. Queens are attracted to the milkweed clan for both the nectar of the flowers and to lay eggs upon for the larvae, just like the monarchs are. Milkweed flowers have a specialized pollination system that even I have a hard time understanding properly. There are usually some specialized bees or flies that take care of it, although there are also generalist ones too that are more easily pollinated by everything wearing black and yellow that may fly past.

A sad little sprig of leaves lies detached from the mother plant a bit downstream of where it formerly grew.

I hate to report that the largest clump of A. nyctaginifolia that was on my property was uprooted and eventually killed by flooding and erosion from hurricane Odile in mid-September 2014.

Exposed cable-like roots of A. nyctaginifolia after a flood and erosion event in 2014. This is the plant from which the leaf spray above came.

What happened was that flooding caused by a dam breach at my water harvesting basins upstream carved a new channel right across where this plant was growing, eroding away soil and exposing the root system. Although I shoveled dirt back over the roots, I believe that the trauma and stress of unearthing it, plus the shallower burial that left it more vulnerable to hot drying sun in summer, was too much and the plant never recovered.

I included this photo to illustrate the span of the root system and to show how relatively thick and fleshy it is (about the diameter of a pencil, and several feet long) for such a modest plant under a foot tall. The photos also serve as a memorial of sorts, because now it’s gone. Additionally, since 2014 I have failed to find a second plant I once knew about, leaving me with only one plant left on my property that I know of. Which is better than zero, but not much.