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Excerpts from Jim Conrad's
Naturalist Newsletter
Entry dated April 19, 2024, from notes taken about 1.5km northeast of Puerto de los Velazquez, Municipality of Pinal de Amoles; N21.138°, W99.667°, elevation ~2835 meters (~9300 feet); oak/pine/fir borderline cloud-forest on limestone bedrock; in the Eastern Sierra Madre Mountains of east-central Querétaro state, MÉXICO
AGERATINA GLABRATA
Atop the ridge, a widely spreading, diffuse, woody shrub with several stiff, sprawling branches had lost the previous season's leaves, but at branch tips new leaves emerged and enlarged. Near the above picture's bottom, right, you can see one of the shrub's three or four small inflorescences.
On this member of the vast Composite/Aster/Sunflower Family, the flowering heads bore no petal-like ray florets along their margins. Above, the heads on the picture's right show several slender, cylindrical, wilted disc florets arising along the heads' perimeters, while the interior of each head is occupied with densely packed white pappus bristles. At the image's top, left, a more mature head opens exposing black, one-seeded, cypsela-type fruits topped by spreading pappuses. Note that each flowering head's pedicel is club-shaped -- thick at the top but gradually narrowing below.
Above it's seen that the scale-like phyllaries comprising the bowl-like involucre subtending the cypselae are of different lengths, and overlap one another. There's no sign of scale-like paleas separating cypselae from one another.
Each cypsela bore about 20 pappus trichomes. The trichomes were slender, or "capillary," but tended to become a little bushy at their tips. A few hairs covered each cypsela, and four ribs ran the cypselae's lengths.
At branch tips, new leaves emerged spottily covered with white, cobwebby stuff. Certain leaf margins were endented with a few obscure, low teeth, like the above, but others displayed no hint of teeth. Blades appeared to contain many tiny, resinous glands, but were hairless, unless the white splotches were composed of minute hairs. Blade venation consisted of two or three secondary veins which arched broadly, avoiding the margins; the end of the lowest veins connected with the second veins' midsections.
The shrub's several slender stems arose from a thick mat of dried pine needles.
I had problems identifying this bush with no fresh flowers. However, when the above pictures were uploaded to iNaturalist, website user "oscargsol," a Mexican Aster-Family specialist, recognized it as AGERATINA GLABRATA.
Ageratina glabrata is endemic to Mexico's central uplands.
The 2011 study by Guadalupe García P. and others entitled "Estudios preliminares sobre el efecto analgésico del extracto de hojas de Ageratina glabrata en dos modelos térmicos de dolor agudo," tells us that in Mexico Ageratina glabrata is popularly known as a painkiller. The authors found that after administering an extract to of the plant to rats, analgesic effects were observed on rats placed on a hotplate.