Silphium asteriscus

I truly enjoy the genus Silphium. It has an exciting yet strangely cohesive range of morphological variation. From humble colonies of S. integrifolium to the stoic and lofty stems of S. laciniatum, from the cool, rough texture of S. terebinthinaceum to the dense flocculence of S. mohrii (see below), they never fail to please.

Here is a veiny crowd pleaser; the leaf of Silphium compositum from northern Alabama.

In the Ozarks Highlands of Missouri, I annually anticipate the lemony blooms of S. asteriscus that begin dazzling the understory of our acid upland woodlands soon after the summer solstice.

Silphium asteriscus (Starry Rosinweed, if you must) occurs throughout the southern United States in acidic woodlands. When young, it produces a basal rosette of ovate to lanceolate leaves. When it bolts to flower, the leaves are alternate along the stem, as opposed to S. integrifolium which is opposite leaved (and which never produces a basal rosette).

In spite of the dramatic range in morphology within the genus, all Silphium have a unique suite of characters. They all have thickish leaves with isodiometric venation (see leaf of S. asteriscus below).

The leaf margins of Silphium are often toothed and each tooth has a yellow callus at the tip (see blurry photo below).

Strangely, species or individuals lacking teeth have calluses on the margins where teeth either were or should be. Most all species have stiffly pubescent leaves and stems. The involucral bracts of the capitula (flower head) are broadly ovate to deltoid in outline and much wider than the closely related Helianthus (sunflowers). Florally, the disk flowers of Silphium are sterile and have only one style, as opposed to Helianthus which has fertile disk flowers with dichotomous styles.

Large or small, laciniate or entire, Silphium is a fine genus. Most every floristic region of eastern North America has at least a couple of species of Silphium (the number increasing to the south and east). As they are beginning to come into bloom throughout the range, be sure to take some time to observe them closely. Feel their cool, rough leaves, their whiskery stems and their stiff phyllaries. You won’t be disappointed.

Comments

  1. Interesting summary of the genus. I really enjoyed seeing the two species in Alabama, even though they were far from flowering at the time. The leaf textures were exciting enough. And I agree... I am never disappointed when I feel the cool, rough leaves, whiskery stems, and stiff phyllaries of a Silphium!

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