Plants of Southern California: Eriodictyon species

Fig. 1. Eriodictyon crassifolium and E. trichocalyx var. lanatum growing together just west of Idyllwild on 6/16/14.

Introduction and Summary
Geographic Distribution of Each Species
Pictures of Each Species


Our Eriodictyon species of trichocalyx and crassifolium have given me a lot of grief over the years, since I have found it hard to reliably determine some specimens. In particular, the things that have given me difficulty are:

Both of the last two bulleted items above reference the net-like pattern in the veins on the bottom of the leaf. However, I've been confused since I often see an obvious net-like pattern on a lot of plants that are vouchered as E. trichocalyx var. lanatum, which is not supposed to have an obvious net-like pattern. And the distinction between tomentose and white-woolly is sometimes difficult, since these states grade into each other.

It appears that a major separating characteristic between E. trichocalyx and E. crassifolium is actually whether the upper surface of the leaf is shiny and sticky, regardless of whether the leaf is glabrous above or sparsely hairy. This sticky characteristic is mentioned in the Munz key, but is only mentioned in the description for E. trichocalyx in the Jepson Manual treatment. However, Abrams comments that varieties nigrescens and denudatum (now combined with nigrescens) appear to connect E. crassifolium with E. trichocalyx. Abrams says for var. denudatum: lvs greenish and glabrate, or even somewhat glutinous above.

Willis Lynn Jepson, in his Flora of California, comments on these two varieties:

In most respects E. crassifolium is constant or fairly uniform in its characters save in thickness of tomentum on the upper side of the leaf, in hue of leaf and in breadth of leaf.

Jepson discusses how the forms can pop up in all combinations and so dismisses the varieties of E. crassifolium.

The last monograph on these species is ancient, by Abrams and Smiley in 1915. In it, they say:

That the two types [sticky and hairy] have sprung from a common stock is also evident, for, as we shall show, there are forms still existing that comprise an almost unbroken series from the glutinous to the tomentose type.


forms of the two groups growing in contiguous territories more or less intergrade where they meet; while in isolated regions, where only one strain is represented, no marked variation occurs even in strikingly differnt environmental conditions.

There are two more recent papers on this genus, that I haven't been able yet to get a copy of, so I only know what it is their abstracts. Ferguson 1998 did a molecular analysis on Hydrophyllaceae to investigate whether that family is monopylletic or not, and probably does not have much detail on the Eriodictyon species.

Hannan 1988 examined the trichomes of all 13 taxa of Eriodictyon, and concluded there were four simple trichomes types: short and straight; intermediate length and straight; long and straight; and long and wavy, with glandular capitate trichomes found in some species. He concluded that most taxa displayed unique combinations of trichome types on stems, leaves, inflorescence axes and flower parts that allowed those taxa to be identified using trichome types alone.

Regardless of my difficulties, voucher determinations seem to show a clear geographic division between the three major taxa: E. trichocalyx var. trichocalyx; E. trichocalyx var. lanatum; and E. crassifolium (including var. nigrescens). Maps of those voucher distributions are shown in the next section, and photographs of the leaf upper and lower surfaces for a number of plants are given in the last section.

Geographic Distribution of Each Species

Fig. 2 shows the geographic distribution of each of these species. I intentionally use the word species here, since E. trichocalyx var. lanatum seems to warrant recognition as the species level since it has a clearly-separate geographic distribution from the main population of E. trichocalyx var. trichocalyx, and is morphologically distinct from var. trichocalyx.

Fig. 2. The geographic range for E. crassifolium from vouchers is given by the red dots (the outliers are almost always misdetermined vouchers or badly-georeferenced vouchers). The range for the other two species is drawn by hand in this map, from the voucher maps for them (see a larger voucher map separately for E. crassifolium; for E. trichocalyx var. trichocalyx, and for E. trichocalyx var. lanatum).

The distribution map shown in Fig. 2 is almost identical to the map given in Abrams and Smiley, except for the disjunct population of E. trichocalyx var. trichocalyx shown in Fig. 2, which does not appear in the Abrams and Smiley map. (Note that it is easy to misinterpret the labels on their map since the species numbers in their key are sometimes different from their species numbers in the descriptions.)

Pictures of Each Species

Click on the pictures to get larger versions.

Eriodictyon trichocalyx var. trichocalyx
Vivian Creek, SnBr, 11/3/09Bertha Peak, SnBr, 6/3/12
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Eriodictyon trichocalyx var. lanatum
Skyline Trail, SnJt, 8/31/12Lower Willows, ABDSP, 11/15/09
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Eriodictyon crassifolium
Chimney Flats, Idyllwild, 6/16/14Pinyon Trail, SnRsMtns, 11/25/12Cactus Spring Trail, SnRsMtns, 2/24/14PCT, near Whitewater Canyon, 1/8/15
Elizabeth Lake area, 4/21/14Chimney Flats, Idyllwild, 6/16/14PCT, near Whitewater Canyon, 1/8/15
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Last update: 11 January 2015