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Tuesday, February 9, 2016

Plant of the Month (February) : Rattlepod – Astragalus trichopodus

Rattlepod (Astragalus trichopodus var. lonchus) - Mother Nature's Garden of Health

Despite forecasts of a strong El Niño season, we’re currently at only about half our normal rainfall.  That’s worrisome!   We’ve been watering Mother Nature’s Gardens, trying to saturate the soils, as they should be this time of year.  One plant that’s blooming right on target is the Rattlepod, Astragalus trichopodus.

Rattlepod is known by several common names including Santa Barbara milkvetch, Three-pod milkvetch, Ocean locoweed and Ocean milkvetch.  We prefer ‘Rattlepod’; a name that well depicts the plant’s most unusual feature.  Three varieties of Astragalus trichopodus grow in Los Angeles County.  Astragalus trichopodus var. phoxis grows in the foothills of the Santa Monica Mountains, but is more common in the inland foothills of Los Angeles County (San Gabriel Mountains).  Astragalus trichopodus var. trichopodus is found on Santa Catalina Island and the inland Puente Hills. 

Astragalus trichopodus var. lonchus – the most common variety in Western Los Angeles County – was once widespread on the coastal plains and Channel Islands (less than 1000 ft. elevation) from San Luis Obispo County to San Diego County and Baja California, Mexico.  Locally, it once grew on the coastal bluffs and coastal prairies of Playa del Rey, Hermosa and Redondo Beach and San Pedro.  Specimens were also collected from the Dominguez Slough (now Gardena Willows Wetland Preserve).  Planting Rattlepod in our Garden of Health brings this plant home.  We hope to use seeds from our garden to re-populate Rattlepod on the Preserve.
Rattlepod (Astragalus trichopodus var. lonchus) - growth habit
Since Astragalus trichopodus var. lonchus is the type grown in our garden, we’ll focus the rest of this article on that variety.  Rattlepod is an herbaceous perennial in the Pea family (Fabaceae).  It dies back to the ground in the dry season, emerging again with the cool rains of winter and early spring.  Once conditions are satisfactory, it quickly grows to a bushy, somewhat sprawling perennial, 2-3 ft. tall and about 3 ft. wide.  Although the stems are stout, they are herbaceous.  The high winds last weekend knocked a few branches off the plant in our garden.
Rattlepod (Astragalus trichopodus var. lonchus) -
compound leaves

The foliage is a bright spring green – the color of garden peas.  Like most in the family, the leaves are compound, with 15-40 rounded leaflets along a midrib that can be up to 8 inches long (see above).  The leaves of local plants are modestly hairy.  We find the foliage to be unusual and attractive in the garden setting.  All parts of the plant are toxic if eaten.   This explains the common name ‘Locoweed’: domesticated horses, cows and sheep can become quite ill if they eat too much milkvetch.

Rattlepod (Astragalus trichopodus var. lonchus) - blooming plant

Rattlepod (Astragalus trichopodus var. lonchus) - close-up of flowers

Rattlepod is an early-flowering species.  It can begin blooming as early as January and almost never flowers later than early April in our area.  The flowers are a waxy cream-white and are arranged around upright stems.   On close inspection (above), the individual flowers exhibit the usual characteristics of members of the Pea family.  You can clearly see the banner and keel on the photograph above.    The early flowers attract bees and other insects.

Rattlepod (Astragalus trichopodus var. lonchus) - green pods

Rattlepod (Astragalus trichopodus var. lonchus) - dry pods

The seedpod of Astragalus trichopodus is rounded and inflated; the dry seeds rattle in dry seedpods, which explains this plant’s common name.  While other vetches have inflated seedpods, Rattlepod deserves special attention; its pods are puffed up like little balloons.  The pods are 1/4" to 3/4" wide and 1/2" to 1-3/4" long.  Green when young, they gain pink tinges as they mature, finally becoming dried and tan (see above).  Each pod contains up to 20 or so, pea-like seeds that become wrinkled when dry. 

Rattlepod is very drought tolerant.  A long taproot partially explains this plant’s  drought tolerance.  But the Rattlepod’s yearly cycle is also geared to our long dry season.  Plants die back to the roots for the dry period – a pretty good strategy for such an herbaceous plant.  For more on drought tolerance see: http://mother-natures-backyard.blogspot.com/2015/10/how-things-work-plant-drought-tolerance.html

Local gardeners on the Palos Verdes peninsula plant Astragalus trichopodus in the hopes of providing larval food for the endangered Palos Verdes Blue butterfly (Glaucopsyche lygdamus palosverdesensis).  We like the plant because it also attracts other interesting insects – pollinators, early butterflies and others.   The flowers and plant are pretty, and contrast well with other native plants.  Rattlepods provide good winter-spring fill around larger plants.  They also look nice with locally native cool season grasses, spring annual wildflowers and Wallflowers. 

Rattlepod (Astragalus trichopodus var. lonchus) - Madrona Marsh Preserve

We are not entirely sure whether Astragalus trichopodus has medicinal value or not.  Asian Astragalus species are used for a variety of ailments, including viral illnesses. Chemicals made by several Astragalus species are being tested as possible cancer and AIDS treatment drugs.  That being said, California native Astragalus species are toxic and should not be eaten.   We’ll just have to wait and see whether compounds from local natives will be added to the medicine bag of the future.

Rattlepod (Astragalus trichopodus var. lonchus) with
Dune Wallflower - Madrona Marsh Preserve

For plant information sheets on other native plants see: http://nativeplantscsudh.blogspot.com/p/gallery-of-native-plants_17.html


We welcome your comments (below).  You can also send your questions to: mothernaturesbackyard10@gmail.com


1 comment:

  1. Thanks for the info. The gardening sheets are good, too. I see the pronunciation is on the gardening sheet, but not in this blog post. So many people get confused about pronunciation - would you consider adding it to these posts?