Plants of Southern California: Salix: Key to Willows of Coastal Southern California Below 6000 Feet Elevation

Determination By Word Key
Determination By Word Key: Print Version
Determination by Pictures


Willows have a reputation for being difficult to identify, and for extensive "hybridization", but it is mostly not their fault, at least below an elevation of ~6000 feet in coastal southern California. In this area, including all of Orange County (Roberts 1998) and all of San Diego County (Rebman and Simpson 2006), we have only five species, and they are very easy to distinguish. Furthermore, you are unlikely to ever run across a hybrid.

Willows obtained their reputation for the following reasons:

Fortunately, George Argus, in the 1993 Jepson Manual treatment of Salix, subsumed the spurious taxa into 5 clearly-distinguishable taxa in coastal southern California. In one stroke, he thereby eliminated the difficulties in keying these species from their leaves and eliminated the vast majority of the putative hybrids. We've keyed out literally hundreds of willows, possibly thousands, using his species delineations and have found exactly one specimen that seems to be a hybrid.

However, the Jepson Manual treatment has to distinguish all 30 taxa in all of California, so this great leap forward in willow identification hasn't been properly appreciated by many botanists in our region. Most botanists in southern California thus never realize how easy it is to distinguish our 5 taxa, simply since they don't have a key to easily do so.

The purpose of this page is to present that key. The key presented here is a vegetative key, based on leaves and leaf buds, that can be used at nearly any time of year, often even with leaves you find on the ground when the plants are leafless.

Actually, once you learn our five species, you won't need the key. You will be able to glance at the twigs and leaves and identify the species immediately, and willows will soon become quite boring from the identification viewpoint.

The key is presented in two ways: first, the usual word key, and second, by using pictures.

The key assumes, of course, that you have a willow you are looking at. In coastal southern California, there is only a single other species you might think is a willow: mulefat, Baccharis salicifolia. (The scientific name means Baccharis with a leaf like a willow!)

The easiest way to distinguish the Baccharis is to look for flowers that are not catkins, fresh or dried, at the tips of the stems. Mule fat will nearly always either be in bloom or have persistent dried flowers which are clearly in terminal clusters. The flowers or remnants can easily be seen to be those of the Asteraceae, sunflower family, but you don't have to categorize them; all you have to do is find terminal flowers. In contrast, willows have blooms that are catkins, a tight cluster of naked stamens or pistils, one to each leaf axil, that leave little evidence of their existence after they drop off.

Another method is to look at the veins in the leaves, best seen on the underneath of the leaf. Willows have one main vein down the center of the leaf whereas mule fat has two additional veins running from the base of the leaf along the outer edge of the leaf. Both have additional shorter veins in a feather pattern branching from the central vein.

There are two other clues that distinguish mule fat from willows, but they are not definitive in separating them like the flower test. First, mule fat leaves tend to be sticky, whereas willow leaves tend not to be sticky. Second, the leaves of mule fat have almost no petiole (leaf stalk), whereas most (but not all) of our willows have an obvious petiole (only narrowleaf willow does not).

There is another plant with willow-like leaves on the desert side of the mountains, desert-willow, Chilopsis linearis ssp. arcuata, but is almost never found on the coastal side of the mountains, and hence won't be discussed here. Flowers quickly distinguish this species as well.

Remember, this is a key to coastal southern California willows below 6000 feet; if you venture above 6000 feet outside of San Diego County, you may find additional species and therefore this key will not apply. However, if you are botanizing in San Diego County, these five species are the only ones in the entire county, which has a maximum elevation of 6533 feet at Hot Springs Mountain.

The relative abundance of these five species is roughly given by the number of vouchers for each of the five species from San Diego County:

# Vouchers% of VouchersSpecies
18942%S. lasiolepis
10724%S. laevigata
9922%S. exigua
399%S. gooddingii
82%S. lucida

Data provided by the participants of the Consortium of California Herbaria (

The above numbers will be representative for vouchers for all of coastal southern California below 6000 feet, since these are widespread species. The abundance of the very common S. lasiolepis is underestimated in the above table since such common species are not vouchered in representative numbers.

For more information, and links to more pictures, see Willow Primer for the San Gabriel Mountains.

Determination By Word Key

Go through this key from top to bottom IN ORDER, and go to the next entry if the previous ones don't find a match. You must go through the key exactly in this order for the first two steps, since the leaves of Salix exigua are variably-colored on the underneath.

Important caveats:

  1. You need mature leaves for the key, since young leaves are often quite different in shape, color and appearance from mature leaves.

  2. You need typical leaves for the key, since willows, like many plants, have no legally-binding contracts to produce identical leaves in all cases. In particular, red willows, S. laevigata, almost always produce a few leaves that are close in shape to those of arroyo willows, S. lasiolepis. These are almost always the first leaves of the season, before it gets better at making its typical leaves. Such specimens are not in general hybrids; this is simply what red willows do, which is probably another source of the belief that willows commonly hybridize.

See the pictures in the next key below to see examples of the traits being discussed.

The key:

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Copyright © 2007 by Tom Chester and Jane Strong
Permission is freely granted to reproduce any or all of this page as long as credit is given to us at this source:
Comments and feedback: Tom Chester | Jane Strong
Last update: 16 January 2007