A growing problem. A member of the sunflower family, stinknet, Oncosiphon pilulifer is also called globe chamomile. It is an oddly attractive but deleterious, distant relative of the familiar medicinal herb. Stinknet is an annual plant from South Africa and grows here in winter like many of our native winter wildflowers. Stinknet leaves, bearing abundant oil glands, have a pungent odor. Exposure to the plant can cause headache, dermatitis, and respiratory problems in some individuals.  It sets seed prolifically, with 300 or more seeds per flower, and in good growing conditions, a hundred or more flowers per plant. One individual plant from a seed spread by shoe, wind or a vehicle, can spawn a colony.  The tiny seeds reside in the soil for years and can survive drought. After good rains in 2024,  2025’s scant winter moisture has kept the populations largely dormant. For now.

Stinknet is a formidable invader. The source of the founder population is unknown, but It was documented in Riverside County in 1991, San Diego County in 1997, Orange County in 2003, and subsequently in Santa Clara County. A herbarium specimen of stinknet from 1997 collected from the Tres Rios constructed wetland in Phoenix is the earliest documented occurrence in Arizona. No connection between the California and Arizona populations has been documented but imported, contaminated feed or straw is the most likely culprit.  It was first seen in Tucson in 2015 at a construction equipment storage site. Stinknet now extends north to Sedona (at 4,200 ft. elevation), south to the border with Mexico, and into Sonora. Only one stinknet plant has been seen in IFNM (in 2023) and it was removed. We remain vigilant and dedicated to keeping it out.

Stinknet is a threat to natural desert and grassland habitat. It colonizes readily on disturbed soil.  It is spread by vehicles and readily observed along roadsides in Maricopa, Pinal, and Pima Counties. Aided by good winter rains, once established it can spread aggressively into undisturbed habitat in open spaces between trees and shrubs and along drainages. Stinknet has no known herbivores. Its pollination biology is unknown but few pollinators have been observed on the flowers.  With the onset of summer, it dies and is extremely flammable. Considered a “ladder fuel” It has been a factor in Arizona wildfires, spreading fire among patches of woody vegetation. Saguaros, paloverdes, and other desert plants are not fire adapted and rarely survive. In subsequent years, stands of stinknet spread, further choking out native plants, and the habitat becomes less supportive of native flora and fauna.

The Friends are fighting back.  In 2025, Friends of Ironwood Forest was awarded a grant from the Overland Expo Foundation to spread the word about stinknet to “overlanders”, those who recreate on public lands on back roads with SUVs, ATVs, mountain bikes, and other vehicles and who use hiking trails, bike paths, and other means to explore public lands and other non-urban spaces.  Public and private land managers lack adequate staff to monitor for stinknet and are eager for help from people who visit their sites. With the support of these grant funds, members of the Friends will be at Overland Expo West in Flagstaff, May 16-18, hoping to enlist some of the 25,000 attendees in the efforts to “see, act, and report” stinknet when they see it.  Following Expo West, the work will continue with recreational clubs in southern Arizona.

Get involved! Stinknet reporting sites, notably stinknet.org for Pima County, map and track stinknet sightings and deploy volunteers to remove it. More eyes to find the early colonizers are critically important: “early detection and intervention” is the optimal strategy for slowing the spread and excluding stinknet. Once it is established, chemical spraying (with collateral death of native plants) and repeated visits over years is the only (bad) option for intervention and may not be practicable.  Parts of Maricopa County have reached that unfortunate impasse.

Local stinknet detection campaigns in Tucson and other areas will reactivate with the onset of winter rains.  If you would like to help monitor stinknet in IFNM and other public lands in Arizona, contact FIF member Chris Flanagan at cflanaga@verizon.net.