Autumn Leaves

Another in a 37 part series whereby I try to edify myself and my loyal readers about the rarefied world of local native botany.  I find that having a better grasp on the terminology makes identification easier and more rewarding.  These are all plants I saw on a short hike starting at the OVLC Ventura River Preserve Old Baldwin trailhead on a 2.5 mile loop.  A few of these are currently dormant, you’ll have to use your imagination.

If you’d like to follow along, all of the detailed botanical descriptions come from the UCLA links provided at the bottom of the Santa Monica Flower Finder database pages.  They are intimidating at first but just take it term by term.

Western sycamore

Let’s start with simple leaves (as opposed to compound).  This leaf shape is known as palmate, easy to remember as it has finger-like features, often 5 (sometimes 3 or 7).  The indentations between the fingers are called sinuses.  Sycamore is deciduous, the leaves are dropping as we speak.

Salvia mellifera – Black sage

Leaf arrangement along the stem is an important feature in identification.  The two main types are opposite and alternate.  Sages, and most of the mint family (go look at your backyard basil or oregano) have opposite-arranged leaves, meaning that from each node along a stem 2 sets of leaves shoot out at a 180 degree angle.  Another important distinction in leaf arrangement is decussate versus helical.  Sage is decussate, meaning that each set of leaves as you move up the stem is at a 90 degree angle to the one above or below.  Helical (like DNA!) tends to twirl more.

Hoary ceanothus- Ceanothus crassifolius

Looking at another plant with opposite leaves.  The hoary ceanothus can be decussate or helically arranged.  A distinct feature that (finally) helped me identify this ceanothus versus our other 3 white flowered ones is the enlarged stipule.  A stipule is the warty lump at the base of the leaf where it meets the stem.  Ceanothus crassifolius leaves have two bulbous stipules, often touching the two on the opposite side.

Green-bark ceanothus

Here is a ceanothus with alternately arranged leaves, generally helical.  The leaf shape is called elliptical, which I would describe as football-shaped.  They can also be oblong, which is kind of elliptical but with somewhat parallel sides, or obovate, tear-drop shaped with a tapered stem.

Toyon – Heteromeles arbutifolia

Toyon leaves are helically alternate, with small stipules.  The blades are elliptic and serrate.  I know you folks can figure that one out… Serrate, like your bread knife, with small saw-like teeth pointing upwards.  The vein arrangement on the leaf face is called pinnate, meaning parallel pairs of veins emerge from the main center rib.

Laurel sumac

Helically alternate leaf arrangement without stipules, petiole and midrib ridged and often red.  Don’t panic, a petiole is simply a plant nerd’s term for a stem, that which attaches the leaf blade to the plant.  They can be many shapes and sizes, and may not be present at all which is known as sessile.  On the laurel sumac they are quite reddish, as are the veins and margins of the leaf, an easy way to differentiate it from a toyon.

Narrow-leaf milkweed

OK sorry, these aren’t on the trail, but they are a great example of a whorled leaf arrangement (as opposed to opposite and alternate).  So far we’ve only had 1 or 2 leaves emerging from one node on a stem, whorled leaves have 3 or more.  Look closely at the hair-like stipules.  Stipules also come in many shapes and sizes.  The leaf blades are lanceolate in shape… I know you can figure this out… Yup, long and lance-like often slightly wider in the middle.

Coastal buckwheat – Eriogonum fasciculatum

Helically alternate, without stipules.  The leaves are linear shaped, which is as needle-like as a non-evergreen will get.  Long and skinny, similar to lanceolate bute without the widened middle.  The underside of the blades are densely tomentose, which means have matted, densely white wooly hairs.

California black walnut

Let’s try some compound leaves before you lapse into a boredom-induced coma.  Walnut’s leaf arrangement is odd-1 pinnately compound.  Which means the numerous (11-19) leaflets are arranged along a central axis.  Odd-1 means there is a single leaf at the end.  The leaflets are lanceolate, though the end leaf is often elliptic, and they are somewhat serrate.  The center stem that holds all the leaflets is called a rachis.

Elderberry – Sambucus mexicana

You’ll have to take my word, these are waiting for first rain to start growing back.  Another compound leaf, odd-1 pinnately compound.  Petioles can be up to 7 centimeters long and are groove-channeled, with the ridges sparsely puberulent.  Another in a long list of terms that basically means “hairy”.  The blades are elliptic to ovate (egg-shaped with a tapered tip), serrate and glossy.

If you made it this far give yourself a round of applause.  And do a rain dance, please.

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