the madrean star thistle

p_rothrockii.jpg

Madrean Star Thistle
Plectocephalus rothrockii
ASTERACEAE

  • upright growing biennial, to 4-5 feet tall

  • purple to pink flowers in summer

  • loved by BUTTERFLIES and other nectar-loving insects

  •  REGULAR WATER (BOTTOM ZONE)

  • best in PART SHADE

  • extremely hardy to negative digits °F

  • grow in CONTAINER or let sprawl up a loose shrub

  • botanical wonder that catches attention

I first came upon this plant in the 1990s when I presume it became available as seed. It still hasn’t caught on in popularity for various reasons. It is a biennial plant, which means it grows for about two years and then goes to seed. When you first plant this mystery species, it looks like a chicory plant or some edible green. Not ugly, just not like much.

But for you botanical nerds and plant-addicts, this species holds a special surprise. Plant this in a partly shaded area that gets regular water, and tucked behind some other showy plants. You may grow it under a widely-branched shrub that allows a good amount of sun through but takes the edge off the summer heat, like a desert willow. This plant will start to rocket up in the summer in an upright manner—usually to about 3-5 feet high, and eventually be covered in what ecologists in our region call the Madrean star thistle. The flower is like the more common garden cornflower or thistle, but with finely divided petals. When it’s in bloom people will ask you what the hell that thing is. Loved by butterflies and bees.

You can find this plant in the mountain canyons of southern Arizona and New Mexico south into Mexico in the Sierra Madre. Formally Centranthus rothrockii.

Katherine Gierlach