Fagonia laevis, California fagonia, and Fagonia pachyacantha, sticky fagonia

Fig. 1. Left: Fagonia laevis, California fagonia or smooth fagonia. Right: Fagonia pachyacantha, sticky fagonia. Click on the pictures for larger versions.

Introduction

This page is mainly a place-holder to show pictures of these two species side by side. Fig. 1 shows the flowers. Fig. 2 shows pictures of the stems, stipules, fruit, leaflets, and baby plants.

A glance at the flowering stems is all you need to separate the species; see the pictures in the top row in Fig. 2. If the plant is not flowering, it may be more difficult to separate the species; one has to use the leaflet shape and the leaf stipules; see below.

Fig. 3 shows the variation in the stem glands for Fagonia pachyacantha that is apparently not well-known; its stems are densely glandular only above, and glabrous below. The Jepson Manual says that the stems have glands on youngest herbage and elsewhere, but it appears the glands are only in the upper part of the stems after the stems have sufficiently matured.

Not all plants in the field, especially young ones, will be as clearly delineated as the ones in the pictures given here. I was very confused the first time I saw plants of F. pachyacantha that did not have flowers or glands on the stem; see Botanical Report for 21 January 2008 to the northeast corner of San Diego County.

In particular, young plants will have similar stems, lacking the obvious glands of more mature plants of F. pachyacantha. The stipules are not always as well-behaved as the ones in these pictures, so you may have to check a number of them, and perhaps on different plants, to be sure which species you are observing. The stipules of F. pachyacantha are 3-16 mm long, compared to the 1-6 mm long for F. laevis, so there is overlap in length, and the stipules of F. laevis are not always obviously curved. The habit difference given in the Jepson Manual is incorrect; both species are subshrubs with similar habit.

Fortunately, there is mostly-complete geographic separation in these two species in the Borrego Desert. F. laevis is found in the western part, west of roughly the longitude of the southeast tip of Coyote Mountain; F. pachyacantha is to the east of that longitude. I can't remember ever seeing the species growing together.

These two species also are different, and somewhat peculiar, in when their blooms are open. F. pachyacantha seems to only open its blooms for an hour or two around noon. F. laevis has a longer open period during the day, but responds to something other than time since it is not reliably open or closed at any time of day.

I've collected some data on when the flowers are open or closed. F. pachyacantha was observed to be open at 11:55 a.m. and 2:21 p.m., half-open at 1:15 p.m., and closed at 4:15 and 4:35 p.m. F. laevis was observed to be open at 9:30 a.m., 11:34 a.m., 1:10 p.m., 1:30 p.m.; just opening at 10:44 a.m., half-closed at 5:31 p.m., and closed at 4:00 p.m., with these observations mostly in February and March, but some in December and January. All times are standard time.

The species were named for their stem hairs. F. laevis has non-glandular stems that appear smooth to the naked eye (laevis means smooth), but belying the name, the stems often are scabrous (having very short hairs that make them feel rough), and sometimes have minute glands. F. pachyacantha was named for its thorny leaf stipules (pachyacantha means thick spined).

F. laevis was much more abundant in 2005 in the Borrego Desert than it has been ever since then, due to the low rainfall in those years. Hillsides used to be covered with these plants, such as the south face of Coyote Mountain, and I'd see it regularly, just as described in Terrestrial Vegetation of California, Third Edition, p. 662:

On dry, hot rocky slopes, F. laevis becomes common to the degree that in the dry season it may appear to be the only living plant on the slope.

After 2005, it soon became nearly absent from many places where it had been abundant. I have hope that if it ever rains well again in the Borrego Desert, it will reappear in those areas and become abundant again, at least until the next drought period.

Fagonia laevisFagonia pachyacantha
Fig. 2. Left: Fagonia laevis. Right: Fagonia pachyacantha.
Top row: Photographs showing the stem and leaf stipules.
Second row: Young Fruit. Note that the orientation is quite variable for both species, as shown in the top row.
Third row: Leaves.
Bottom row: Seedlings.
Click on the pictures for larger versions.

Fig. 3. Two pictures showing the glabrous stems in the lower part of the stems of F. pachyacantha, and the densely-glandular stems in the upper part of the stems.
Click on the pictures for larger versions.


I thank Aaron Schusteff for permission to use his stem photograph of F. pachyacantha.


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Copyright © 2016 by Tom Chester
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Comments and feedback: Tom Chester
Updated 5 February 2016