Jonathan Curley found an oddity near San Francisco earlier this month. It looks like Aphyllon franciscanum, Yellow Clustered Broomrape. However, there’s something peculiar about this particular yellow plant.

Two clumps of Aphyllon franciscanum in the same patch of dry grass and litter: in the foreground, a vivid pink-magenta clump of leafless, hairy stems and tubular flowers; behind it, a second clump in the typical yellow-orange form.
Aphyllon franciscanum by Jonathan Curley / iNaturalist CC BY

Aphyllon franciscanum — GBIF occurrences

Data: GBIF · Map: © OpenStreetMap contributors

If you want to see Aphyllon franciscanum, then western North America is the best place to be, particularly around the coast. The native range runs from southwestern British Columbia down the coast to Baja California. It runs east to beyond the Rocky Mountains, but populations are much sparser to the east. It’s particularly common around San Francisco, which explains the epithet. The first part, Aphyllon, means leafless. It’s found in serpentine soils and coastal sage scrub.

A clump of Aphyllon franciscanum: about a dozen leafless, hairy yellow stems rising from gritty red-brown soil between pale rocks, each topped with a curving tubular flower in yellow and rust-brown. Green chaparral and dark blackened branches in the background.
Aphyllon franciscanum by oxalismtp / iNaturalist CC BY-NC

Another thing you’ll want to look for, if you’re searching for Aphyllon franciscanum, is a host plant. Broomrapes are parasitic plants and have no chlorophyll, meaning they’re dependent on other plants for food. The plants wait in the soil to sense root exudates from hosts. When they sense the chemicals they strike, attaching themselves to the roots to steal water and food from their host. These are usually Eriodictyon and Eriogonum, but also Eriophyllum and Phacelia. It’s this ability to parasitise other hosts, and avoid Artemisia, that helped botanists identify it as a separate species from its close relative Aphyllon fasciculatum in 2021.

Close-up of a single Aphyllon franciscanum flower: a bright yellow two-lipped bloom, two smaller lobes above and three larger lobes below, the petal surfaces and edges fringed with fine white hairs and marked with deeper yellow veins. A second flower sits out of focus on the right, with a brownish calyx visible behind.
Aphyllon franciscanum by Ken-ichi Ueda / iNaturalist CC BY

If you’re looking up information about it, it’s not just Aphyllon fasciculatum you’ll need to bear in mind. The genus Aphyllon has only fairly recently been accepted. Until 2016, you’d see Aphyllon species listed as Orobanche, so you’d originally see it described as Orobanche fasciculata var. franciscana.

A close-up of an unusual Aphyllon franciscanum flower: the same two-lipped, hairy form as the typical species, but with the lobes flushed dusky red-purple rather than yellow. A patch of yellow still shows in the throat. Held between a thumb and finger, with dry soil and litter out of focus behind.
Aphyllon franciscanum by planetboom / iNaturalist CC BY-NC

This is a plant where observations on iNaturalist have played a big role in getting the species recognised. In their article dividing Aphyllon franciscanum from A. fasciculatum, Schneider and Benton mention using 87 iNaturalist observations made between 2009 and 2020. Those observations keep coming in. The photo by Jonathan Curley is one of a few showing that the flowers of this plant don't have to be yellow, showing that the species has more to reveal than the name suggests.

Cover image: Aphyllon franciscanum by Radd Icenoggle / iNaturalist CC BY-NC