Yellow starthistle, sea lavender and poison oak: a July 2022 Bay Area botany report

Poison oak may be the greatest hazard for botanists working in the San Francisco Bay Area national parks, yet the team’s July 2022 newsletter argues it deserves some reverence. The issue also tracks three invasive plants. It comes from the San Francisco Bay Area Inventory and Monitoring Network (SFAN) Botany Program, which has two teams: Plant Community Monitoring (PCM) tracks long-term changes in vegetation structure and composition, while Invasive Species Early Detection (ISED) maps, assesses and promptly reports priority invasive plants along trails and roads, and treats infestations when feasible.

What the July surveys found

• Rancho Corral de Tierra and the Presidio (Golden Gate National Recreation Area). The ISED team began monitoring in the Presidio, covering most of Crissy Field and Fort Mason. It is dense with invasive plants such as Rubus armeniacus and Hedera helix. Near Crissy Field the team detected new single occurrences of Algerian sea lavender and oppositeleaf Russian thistle.
• John Muir National Historic Site. A baseline survey at Mt. Wanda found yellow starthistle in high abundance. A John Muir natural resources staff member told the team the plant was not present there in the 2021 growing season and suspected the new dense patches were partly due to extreme rainfall in October and November 2021. In July 2018 the newsletter had reported small, isolated patches in the Marin Headlands and Point Reyes National Seashore, and predicted the plant’s range and abundance would expand toward the coast over the next 30 years as the climate changes.
• Freshwater marsh monitoring (PCM). Chest-high sedges hid plot markers, and cattle left flattened vegetation, deeply cut trails and grazed plants. Grazers seemed to favour the flower clusters of brownhead rush, and small herds sometimes wandered into the plots.

Yellow starthistle

Centaurea solstitialis is a close relative and lookalike of tocalote, the previous issue’s feature. Both have ball-like flowers with fluffy yellow tops, branching stems and narrow, erect leaves. The differences:

Both are toxic to horses and other grazing animals because of a compound called repin. With continued ingestion, symptoms resemble Parkinson’s disease, and the animal eventually starves because of paralysis of the lips and tongue.

Two plants of the salt marsh

Algerian sea lavender (Limonium ramosissimum) grows in coastal salt marshes, coastal scrub and riparian scrub, and is one of the few invasive species able to grow in salt marsh. It is native to the European Mediterranean and was brought over as an ornamental, then escaped. It has small, dense basal leaves, several erect stems per plant and clusters of small white to purple flowers from June to August. Each plant drops thousands of seeds that float on the tides and stay viable for weeks, which makes populations hard to track if not managed in time. Small populations exist around San Francisco Bay, but this season only one occurrence was documented, at Crissy Field. Do not mistake it for the native California sea lavender (Limonium californicum), which has much larger leaves and overall stature but lives in the same habitat.

Limonium ramosissimum at Crissy Field, where one occurrence was documented this season. NPS / Katherine Stratton

Oppositeleaf Russian thistle (Salsola soda) is a small, fleshy, hairless shrub of salt marshes, mudflats and the upper intertidal zone. Its leaves are opposite near the base and alternate toward the top, and it blooms from July to October. It is also called agretti and is used in pasta dishes, which makes it a popular vegetable even though it harms Bay Area wetlands. Germination success is low, but the plant then grows rapidly. Its seeds float and can germinate where there is almost no soil, and bikes and shoes can carry them along the many waterside trails.

A word for poison oak

Toxicodendron diversilobum is the plant the monitoring crews most want to avoid, but the newsletter calls it an ecological powerhouse that provides forage and habitat for native wildlife:

• Flowers support pollinators, and persistent berries feed birds and other animals all year.
• Browsing mammals and insects eat the nutrient-dense leaves without ill effect.
• Roots give small mammals a place to burrow, leaves supply material for bird nests, and the shrub shelters many animals from predators.
• It can outcompete some invasive species, resprouts quickly after fire, and is even grown in some nurseries for restoration.
• Per the U.S. Forest Service, it is the most widespread shrub in California, in many habitats west of the Sierra Nevada and Mojave Desert.

The team still advises learning to recognise it on sight and not touching it. Its growth form and colour vary widely with habitat and season, which is what the species name diversilobum hints at. It blooms from March to June.

Poison oak. NPS / Katherine Stratton

Sources

• National Park Service, San Francisco Bay Area Inventory and Monitoring Network, Botany News – July 2022, a newsletter issue compiled by a botany program intern; rewritten in hubnx's own words.