Native Plant Showcase: Ageratina altissima (white snakeroot)

By Lise Fracalossi

Next up on our list of planted species alphabetically is Ageratina altissima, or white snakeroot.

… I feel a bit intimidated tackling this one, as it’s the first member of the Asteraceae family that I’ve written about. Asteraceae is an enormous and complex family – but we’ll get to that.

By the Numbers

Species: Ageratina altissima (formerly Eupatorium rugosum)

Common name(s): white snakeroot, richweed, white sanicle

Family: Asteraceae

Seed source(s):

Flower Appearance: Tiny white flowers are topped with white “streamers” and bundled into clusters. Each cluster is borne on a short stalk from the central stem, forming a flat or rounded top.

Many white flower clusters with streamer-like tufts atop them.

Ageratina altissima flower clusters

It’s always a party when you’re white snakeroot.

Leaf/stem appearance: The leaves are simple, toothed, and somewhat heart-shaped. They are arranged oppositely on the stem.

Fruit: Each of the tiny flowers, if pollinated, develops into a cypsela, a one-seeded dry fruit formed from the ovary and the fused sepals. This is characteristic of family Asteraceae.

Habitat: While it prefers forests, especially rich, damp ones along rivers, it can also be found on roadsides and other disturbed areas.

Native To: All of New England (in most counties) plus New York, in ecoregions 58, 59, 82, 83, 84.

Light: Shade to part-shade

Moisture: Medium-wet to medium-dry soils.

Height: 2-3'

Spread: 2-4'

Blooms: July, August, September, October

Wildlife Benefit: White snakeroot is a larval host for many butterflies and moths, including the ruby tiger moth and the dramatic-looking clymene moth, among others. It provides late season food (pollen and nectar) to numerous insects, including many native bees.

Fun Facts About Asteraceae

Before we get into the unique features of Ageratina altissima, let’s talk about the family it’s in, Asteraceae.

The family is, as the botanists say, “really fucking complicated.”

This is largely because Asteraceae is one of the most recent families, evolutionarily speaking, having first evolved some 85 million years ago (mya). This is young compared to the magnoliids (some of the earliest flowering plants), which date to 150-180mya. By that time flowering plants had figured out some shit as far as reproductive strategies.

It’s also a vary large family. Many common garden plants are in Asteraceae, and not just things we call “asters.” This includes both food crops (lettuce, artichoke, chamomile, sunflowers, etc) and decorative flowers (black-eyed Susan, marigolds, etc).

It also includes plants we label weeds, both native and not: eg. goldenrod (Solidago), dandelion (Taraxacum), and chicory (Cichorium).

Some unique things about asters include…

As I alluded to in the section above, Asteraceae usually have composite flowers – in fact, it’s also known as family Compositae. This means what we call the “flower” is actually a bunch of tiny flowers, grouped together into a structure called the a capitulum (or “head,” if ya nasty). These are then wrapped in a set of modified leaves called phyllaries, like a little bundle of botanical complexity.

If you ever wonder why I hedge these statements with “often,” “usually,” and “typically,” it’s because plants are weird and there always corner cases.

But each of the tiny florets is a complete flower in its own right, and yes, I do mean that in the botanical sense, where each floret has both male and female reproductive structures.

  • Asteraceae often have two types of flowers, ray and disk flowers. If you think of a daisy, the disk flowers are the ones that form the central yellow disk, and the ray flowers are the white ones that radiate around the center, like rays of the sun.
Photo of an oxeye daisy, Leucanthemum vulgar, with white ray flowers, around a cluster of yellow disk flowers

Oxeye daisy, Leucanthemum vulgare.

Oxeye daisy, Leucanthemum vulgare. Photo by and (c)2008 Derek Ramsey; taken at the Chanticleer Garden

This pattern is in fact what gave the family its common name – “aster” after the Greek and Latin word for “star.”

(Obligatory dad joke: is a lack of asters a dis-aster?)

  • Asteraceae requires a unique set of botanical jargon, over and above the normal botanical jargon. This is why I’m intimidated by them! You think you’re getting the hang of this whole “botany vocabulary” thing, and then you have to learn words like “pappus,” “phyllary,” and “involucre.”
Hey baby, nice phyllaries.

Hey baby, nice phyllaries.

Fun facts about Ageratina altissima

You know how I just talked about ray and disk flowers?

… yeah. About that. Ageratina only has disk flowers. Because plants, that’s why. Between 11-20 of these flowers are stuffed into a single cluster, and each plant can have dozens of clusters.

All parts of Ageratina are poisonous to humans, cattle, and horses. This is due to a phytochemical called tremetol. This can contaminate the milk of dairy cows and be passed on to humans, causing something called “milk sickness.” It’s said that Abraham Lincoln’s mother died of this, as the cause would not be known to European Americans until the 1830s.

Oddly enough, the common name comes from the fact that European colonists first thought it cured snakebite. Allegedly some native (Shawnee) woman took pity on us and taught us better.

White snakeroot spreads aggressively. (Just like sneks, amirite?) Given all those flowers on a single plant, you can imagine how! If that weren’t enough it also spreads asexually, via rhizomes, especially in disturbed soil.

For this reason, Wild Seed Project recommends planting it in areas where you’ve removed invasives and want something that can outcompete them.

There is so much more to say about Ageratina – I learned so much writing this! – but that’s where I’ll leave it for today, as my fingers are tired from writing “Asteraceae” so many times.

Photo of Ageratina altissima, a plant of 3-4' with white tufted flower clusters and simple green leaves

Ageratina altissima at Ausable Chasm, Keeseville, NY, August 2019

References and Further Reading

Ageratina altissima on…

Asteraceae on…

My iNaturalist observations:

Other:

All photos, including the banner image, are by Lise Fracalossi unless otherwise noted.