Mule Fat

Mule fat (Baccharis salicifolia) is a lanky shrub with bright green, somewhat sticky leaves. It is a riparian species – a species that requires a regular or semi-regular source of fresh water. It grows throughout the Reserve near seeps and run-off channels, often with willows, which it resembles.

Mule fat bears male and female flowers on separate plants. Most of the year, both types of flowers can be found, as can the fluffy seed heads. Each puff of wind sends hundreds of silky, seed-bearing parachutes adrift over the Reserve.

Description ^2,4,11,26,59

Mule fat is an evergreen shrub, usually less than 10 feet (3 m) tall. Numerous simple, flexible branches extend up from the base. Leaves are 2-6 inches (5-15 cm) long, lance-shaped, often shiny with resin. Margins are toothed or smooth. Leaves are easily confused with leaves of arroyo willow (Salix lasiolepas), with which mule fat is often associated.

Mule fat bears male and female flower heads on separate plants (dioecious). Flower heads are composed of cream to white disk florets and are arranged in terminal clusters. Floret structure can be difficult to interpret with the naked eye. Each male floret has a conspicuous but non-functioning female stigma and style. The stamens of the male floret are united into a tube around the style. Together, these protrude from the floret giving the entire flower head the spiny appearance of a mace, the club used in battle by knights of old. The female floret resembles a paintbrush due to numerous fine hairs (the pappus) that surround the slender style and two-parted stigma. Ultimately the pappus will form the parachute that disperses the seed. The main flowering period is late summer through early spring but flower heads may be found all year.

The species name of mule fat, salicifolia. loosely translates as “willow-leaved”. Indeed, it is easy to mistake mule fat for arroyo willow, especially as they are often found together. The clusters of small disk florets of mule fat are unlike the fuzzy catkins of willow. In the absence of flowers, they may be distinguished by leaf characteristics. The mature leaves of mule fat are resinous, which makes them shiny, and they are the same color on both surfaces; the mature leaves of arroyo willow have a duller surface and are paler below. The leaves of willow, like leaves of most species, have a single, central vein running the length of the leaf. Mule fat leaves often have three parallel veins, one central and two close to the margins.⁵⁹ The marginal veins can be hard to see in young leaves.

Classification  

Mule fat is a dicot angiosperm in the sunflower family, the Asteraceae.² This is the largest family of vascular plants in the Northern Hemisphere.¹⁴³ “Flowers” of Asteraceae are made up of one or both of two types of flowers (florets): symmetrical disk florets and strapped-shaped ray florets. These are crowded onto a common base (receptacle), which we call a flower head,^11,44,49 and which is often assumed to be a single flower. Other familiar Asteraceae that occur in the Reserve include such dissimilar flowers as Bush Sunflower (Encelia californica), Goldenbush (Isocoma menziesii) and California Sagebrush (Artemisia californica).

Baccharis is the only common genus in the Asteracea that is dioecious (has male and female florets on separate plants).¹¹ Species in the genus Baccharis have disk florets only.

Two other species of Baccharis, Coyote Brush (B. pilularis) and Chaparral Broom (B. serathroides) are also found in the Reserve.⁴⁸

The Jepson Manual² lists only one subspecies, spp. salicifolia.

Ecology  

Mule fat is one of the early colonizers of riparian areas.¹¹ Mule fat seeds germinate rapidly in areas recently de-vegetated by flood, fire or other disturbance.⁵⁹ Together with arroyo willow (Salix lasiolepas), mule fat forms dense thickets that are slowly replaced by taller willows and cottonwoods.¹¹

Human Uses  

In California, mule fat was widely used by Native Americans to make hand fire-drills.^15,17,34 The tip of a thin, vertical stick was rested in a shallow cup and rotated quickly between the hands. The resulting friction produced sparks that ignited dry tinder.¹⁵ Other Californian Indians used mule fat for arrows and spears.³⁴

Kumeyaay used mule fat as thatching material and made a poultice from cooked leaf and bud-tips.³⁷ They also made box traps for quail.³⁴ According to one report,³⁴ a trap sometimes caught so many birds that the quail flew away with the trap.

Interesting Facts  

Although the common name implies that mule fat has been used as forage for livestock,^8,23,71 there is some disagreement. One source says it was used only as a last resort during periods of drought,¹¹ and another attributes the name to the fact that mules become bloated after consuming it.³⁴ Yet another source says the “fat” in the common name comes from the sticky resin in the leaves.³⁵

Occasionally, mule fat leaves will be found covered with tiny yellow-green bumps, 1/4 inch (1-2mm) across, often with a dimple on top. These are the blister galls of a tiny mite, distantly related to spiders.²²