Dogweeds and Pricklyleaves
I don’t know who goes naming all these plants, but some of these people must be very basic. Dogweeds are gorgeous little daisy plants with powerfully scented foliage (scents range from smelling like parsley to tarragon, depending on the species). The name “dogweed” isn’t meant to be complimentary. But if these people associate dogs with ugliness, they are indeed misled people because dogs are gorgeous creatures.
Many of the dogweeds are annuals but the ones we grow are perennials. These plants were, at once, all in one genus called Dyssodia. But as more genetic evidence improved our understanding of the relationship of these plants (evolutionarily) and they had to be split into Adenophyllum and Thymophylla.
Thymophylla is the most common of these genera in the nursery trade and since they have been split from Dyssodia, are easier known by the common name pricklyleaf. The five-needle pricklyleaf or as better known in the nursery trade, golden fleece (Thymophylla pentacheata), is most common. It is often found in 6-packs or 4 inch pots with pansies and petunias.
All these species, in the daisy family (Asteraceae), are wonderful nectar plants and will especially attract butterflies. Five-needle pricklyleaf (Thymophylla pentachaeta) is the larval food plant for the dainty sulfur (Nathalis iole). All of these species also have a long history of medicinal use by people of the past as well as the present.
The species listed below are the ones you’ll most likely find to put into your landscape. Most of them are rare in the trade, but we are working on changing that. Five-needle pricklyleaf is common in the nursery trade.
Not all that long ago, while we were hiking, we came across this plant. We found it in a hill between A Mountain and Tumamoc Hill in Tucson. What was most intriguing about the plant was the odor, which smelled much like the Lemmon Marigold (Tagetes lemmonii). At first I thought we were dealing with a Tagetes species that I didn’t know. Later we figured out that it was San Felipe Dogweed (Adenophyllum porophylloides).
When you’ve been at this a while, you forget things. I thought this was my introduction to this entire genus, but a few weeks later remembered that back in the 1990s I was working on a rare plant called Wright’s dogweed (Adenophyllum wrightii) for the Nature Conservancy—it is one of Arizona’s rarest plants. During the 90s, little was known about this species and specimens from the herbarium dated back half a century. But in the early 2000s it was sighted again. The rareness of this annual Adenophyllum was due to its dependency on ephemeral pools, tank-like collections of pond-like water that collect from summer rains. This species is dependent on those pools and to witness the species you must be at the right place at the right time.
You won’t see Wright’s dogweed anytime soon in nurseries. But you MIGHT find some of the other Adenophyllums, especially the aforementioned San Felipe Dogweed. These species can do well in cultivation, and can take full to part sun. The San Felipe dogweed is found in both rocky soils as well as in riparian washes.
The pricklyleaf plants are probably much more familiar. Easily found in nurseries, they are also known as golden fleece or just dogweed. Thymophylla pentacheata is the most commonly available. Rarely, most likely in a native plant nursery, you may find American pricklyleaf (T. acerosa).
You can plop either of these in the ground once, and they will become permanent residents. This isn’t only because they are perennial plants—they also function like wildflowers, and will reseed themselves about the landscape. Because they are small, low-growing plants, they aren’t intrusive and if unwanted in a particular location, are easy to eliminate.
Most of these species take full to part sun with moderate to low water.
How to tell the two pricklyleaf species apart: T. acerosa has simple, linear, needle-like leaves 1-2 cm long, and sessile to subsessile flowers that are embedded in the foliage, while T. pentachaeta has leaves that are pinnately divided into 3-7 needle-like lobes, and flowers that are held above the foliage on peduncles 2-10 cm long. T. pentachaeta is also usually not as robust as T. acerosa. If you can’t tell, just say it’s T. pentacheata and you will probably be right.
One other Thymophylla worth mentioning is the Sonoran pricklyleaf (T. concinna). It’s an annual and has cute flowers much like a blackfoot daisy (Melampodium leucanthum) but with plump thinly-lobed leaves that stand erect along the stems, giving this plant a somewhat bristly or bottle-brushish look. It’s unlikely you’ll see it for sale, but if you happen to be hiking in Organ Pipe National Monument where they are common, you will know what you are looking at.