Plants of Southern California: Lycium species of the San Diego County Desert
Introduction
Table 1: Unique Characteristics of Each Species With Pictures
Carla Hoegen and Fred Melgert's Key
Comparison of L. brevipes with L. parishii
Numerical Analysis
Photographs
Distribution
Some Web Links
Note on Lycium torreyi
Things to Add to This Page in the Future
Introduction
Lycium species are difficult to identify in some cases for at least four different reasons:
- The key to determine specimens uses both flowers and fruit, and often all one has are flowers.
- One major couplet in the 1932 Hitchcock key used in Munz and the Jepson Manual, using the ratio of the calyx lobes to the calyx tube and the calyx lobe length, is often indeterminate, with some specimens satisfying both branches.
- The key uses the hairiness of the calyx and leaves, and some specimens do not appear to have read the key and might be easily keyed under the "wrong" hairiness.
- The measurements given in the floras of the leaf lengths and widths, and the calyx tube and lobes, often do not give the full range for all species.
- The flowers quickly fade and shrink in voucher specimens, making it difficult to determine colors and corolla lobe lengths.
Fortunately, we have just five Lycium species (see note below) in the desert portion of San Diego County (according to the Checklist of the Vascular Plants of San Diego County, Jon P. Rebman and Michaal G. Simpson, 4th edition, 2006), and they each seem to have one or more unique characteristics that immediately determine them, except for two species that require the combination of two characteristics to distinguish them.
Table 1 gives the unique characteristics, along with a picture showing those characteristics. Most of the botanical terms are illustrated in the picture, and all are explicitly defined below the table. The non-plant parts in some of the pictures are human fingers.
Table 1: Unique Characteristics of Each Species With Pictures
Definitions of some of the botanical terms used here are given below.
| Species | Unique Characteristics | Picture | |
|---|---|---|---|
| L. andersonii | Corolla tube = (4-7) x calyx tube AND calyx glabrous (without hairs). All other species except L. fremontii and L. parishii have a ratio of less than 4. Those two species have ratios of 2-5, but they have glandular-pubescent calyces.
In the picture on the immediate right, on my screen, I measure the corolla tube as 42 mm and the calyx tube as 8 mm, for a ratio of 5.2. You should get the same ratio, even if your screen size is different. | 
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| L. brevipes var. brevipes | Corolla lobes = (0.45 - 0.75) x corolla tube; the other species usually have a ratio of 0.15-0.38.
# of calyx lobes and corolla lobes usually 4, with some flowers having 5 lobes; the other species almost always have 5 calyx and corolla lobes (L. fremontii also sometimes has 4 lobes). If you see a flower with just four lobes, you should immediately think of L. brevipes and check the ratio of the corolla lobes to corolla tube to verify. L. brevipes is likely only to be confused with L. parishii, but the ratio of the corolla lobes to corolla tube easily distinguishes the two. See a detailed comparison below. In the picture on the immediate right, I measure the corolla lobes to be 20 mm and the corolla tube to be 40 mm, for a ratio of 0.50. |  | 
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| L. cooperi | Corolla greenish-white; the other species are a pure white to pink to purple
Fruit greenish-white, constricted at top; the other species have red fruit without any constrictions | 
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| L. fremontii | Calyx lobes short, not appearing leaf-like AND Plant densely glandular pubescent.
Only L. andersonii also has short calyx lobes, but it has a glabrous calyx and usually has a much longer corolla tube relative to the calyx. The ratio of the corolla tube to the calyx tube is 1.9-2.4 in the pictures, but I have observed flowers with a ratio of 5.4 in Fossil Canyon in Imperial County. The dense stalked glands are visible as the "little balls of goo" on tiny stalks, and often glistening in the light. The white lines point to only a small number of the glands. The glands are sticky, and often have attached objects, such as the dandelion fluff in this picture. In the other picture, the glands are visible mostly as white dots. | 
Picture copyright © 2004 by Michelle Cloud-Hughes | 
Picture copyright © 2008 by John Marquis |
| L. parishii | Calyx lobes leafy, about as long as the calyx tube AND plant slightly- to densely-glandular pubescent. The other species are without hairs, to moderately hairy, usually without glands, except for L. fremontii, which has short calyx lobes that do not appear leaf-like.
L. parishii is likely only to be confused with L. brevipes, but the ratio of the corolla lobes to corolla tube easily distinguishes the two. See a detailed comparison below. The ratio of the corolla tube to the calyx tube is 2.9-3.5 in the pictures here; this picture has a ratio of 4.4 and shows the glands more clearly. | 
Picture copyright © by J.S. Miller | 
Picture copyright © by J.S. Miller |
Definitions of the botanical terms used above:
The corolla is what most people refer to as the flower, the showy white to purple part. The corolla consists of a tubular lower portion, the corolla tube and the 4-5 lobes at the tip. Botanists consider the lobes to be the free (not connected) portion of the petals, which are fused into the tube below the lobes.
The calyx consists of the green bracts at the base of the corolla, surrounding it there. It also consists of a tube and lobes.
The fruit is like a little tomato, a berry that is either green or red.
Pubescent refers to hairs that can only be seen by a magnifying glass, although often when botanists refer to a plant having hairs it can mean either hairs visible to the eye or smaller ones. Glands are hairs with balls of goo at their tips.
Carla Hoegen and Fred Melgert's Key
1. Flower greenish-white ... Lycium cooperi, Cooper's desert thorn.
1' Flower not greenish-white
2. Plant glabrous, with long exposed corolla tube ... Lycium andersonii, Anderson's desert thorn.
2'. Plant glandular/hairy.
3. Calyx lobes short, saw toothed, not appearing leaf-like ... Lycium fremontii, Fremont's desert thorn
3'. Calyx lobes leafy
4. Calyx lobes glandular; sandy to rocky slopes, canyons ... Lycium parishii, Parish's desert thorn.
4'. Calyx lobes not glandular, a bit spreading; flowers relatively big; low elevations ... Lycium brevipes brevipes, Common desert thorn.
Comparison of L. brevipes with L. parishii
Numerical Analysis
I used my photographs, and those on Fred Melgert and Carla Hoegen's pages of L. brevipes and L. parishii, to measure the lengths of the calyx tube, the calyx lobes, the corolla tube, the corolla lobes, and how exserted the stamens were from the base of the corolla lobes. I also noted the number of corolla lobes. I used only flowers photographed from the side where I could see the base of the calyx. I measured nine flowers of L. brevipes and seven flowers of L. parishii where I could see and reliably measure all those characteristics. I normalized all the measurements by using ratios. All of the measured photographs are shown in Fig. 2.
Fig. 1 shows how exserted the stamens are vs. the ratio of the corolla lobes to the corolla tube L. brevipes and L. parishii. The measure of exsertion was the ratio of the {length of the stamens beyond the base of the corolla lobes} to the {length of the corolla lobes}.
Fig. 1. A plot of how exserted the stamens are vs. the ratio of the corolla lobes to the corolla tube for L. brevipes and L. parishii.
The species separate cleanly on the ratio of the corolla lobes to the corolla tube, with values of 0.48 to 0.70 for L. brevipes and 0.21 to 0.37 for L. parishii. See Fig. 2 to get a visual impression of what these ratios mean, and Fig. 3 to see the closest specimen of L. brevipes, with a ratio of 0.48, to L. parishii, with a ratio of 0.37.
The species generally separate on how exserted the anthers are, but there is some overlap. Only L. brevipes has a ratio of the anthers to corolla lobes below 0.8, and only L. parishii has a ratio above 1.1. Both species have some specimens with ratios of 0.8 to 1.1.
In addition, the number of corolla lobes was a strong discriminant. Seven of the L. brevipes flowers had four corolla lobes; one had five lobes; and the others had four visible lobes, but might have had a fifth lobe obscured in the side view. In contrast, none of the L. parishii flowers had four lobes.
Photographs
Photographs of flowers of the two species taken from the side are shown in Fig. 2. Each photograph was cropped and rotated to display the flower facing upward, and each was resized to be 200 pixels wide. The photos thus accurately portray at a glance the actual ratio of the flower height to corolla width for the two species.
For each species, the photographs are sorted in ascending order of the ratio of the corolla lobes to the corolla tube, with the ratio given below each photograph. This makes the appearance of the table a bit messy, but it is necessary to show the flowers approximately as they appear relative to each other.
Fig. 3 shows the two specimens which are closest in the ratio of the corolla lobes to corolla tube.
Lycium brevipes | Lycium brevipes | Lycium parishii | Lycium parishii |
|---|---|---|---|
Corolla lobes / tube = 0.48 | 
Corolla lobes / tube = 0.55 | 
Corolla lobes / tube = 0.21 | 
Corolla lobes / tube = 0.24 |
Corolla lobes / tube = 0.57 | 
Corolla lobes / tube = 0.59 | 
Corolla lobes / tube = 0.24 | 
Corolla lobes / tube = 0.25 |
Corolla lobes / tube = 0.61 | 
Corolla lobes / tube = 0.62 | 
Corolla lobes / tube = 0.27 | 
Corolla lobes / tube = 0.28 |
Corolla lobes / tube = 0.62 | 
Corolla lobes / tube = 0.62 | 
Corolla lobes / tube = 0.29 | 
Corolla lobes / tube = 0.34 |
Corolla lobes / tube = 0.65 | 
Corolla lobes / tube = 0.70 | 
Corolla lobes / tube = 0.37 | (intentionally blank) |
| Fig. 2. Photographs showing the flowers of L. brevipes (left two columns) and those of L. parishii (right two columns), sorted in ascending order of the ratio of the corolla lobes to the corolla tube. Photographs from Tom Chester and Fred Melgert / Carla Hoegen. Click on the pictures for larger versions. | |||
Lycium brevipes | Lycium parishii |
|---|---|
|
Corolla lobes / tube = 0.48 (smallest value for L. brevipes) |
Corolla lobes / tube = 0.37 (largest value for L. parishii) |
| Fig. 3. Left: The flower of L. brevipes with the smallest ratio of the corolla lobes to corolla tube for that species. Right: The flower of L. parishii with the largest ratio of the corolla lobes to corolla tube for that species. These are the closest specimens of the two species shown in Fig. 1, and are still visually distinct. Photographs by Tom Chester. Click on the pictures for larger versions. | |
Distribution
Fred Melgert and Carla Hoegen have a wonderful interactive mapping program for these species, collecting data from the Consortium of California Herbaria, iNaturalist, and Calflora. The map for all five species is pretty crowded, so it is best to zoom in on your region of interest, making the distribution clearer.
The link goes to a page showing all five species. If you want only one or two species, simply delete the other names and click on the "magnifying glass" on the right of the box showing the names. You can also select what sources are plotted.
Older distribution information is given in the following table, from vouchers accessed in 2008. The species name is linked to distribution maps from the Consortium of California Herbaria, using data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/):
| Species linked to 2008 voucher distribution map | # Vouchers Borrego Desert / San Diego County | Representative San Diego County Desert Distribution |
|---|---|---|
| L. andersonii | 3 / 73 | Borrego Valley; San Felipe Valley; Vallecito; Jacumba; Mountain Springs |
| L. brevipes | 4 / 13 | Borrego Valley; Clark Valley; Borrego Badlands; northeast corner of County |
| L. cooperi | 0 / 33 | San Felipe Valley; Box Canyon |
| L. fremontii | 1 / 22 | Borrego Valley; Split Mountain; Canebrake Canyon; Fossil Canyon |
| L. parishii | 0 / 8 | Mountain Palm Springs; Vallecito; Fossil Canyon |
Some Web Links
- Project Lycieae by J.S. Miller and R.A. Levin for a key to the North American Lycium species and pages devoted to each species. The pages for our five species are: L. andersonii, L. brevipes, L. cooperi, L. fremontii, and L. parishii.
- Lycium by Richard W. Spjut.
Note on Lycium torreyi
There are four online vouchers of L. torreyi in the San Diego County desert, but it is not accepted as being in the County by Rebman and Simpson. L. torreyi is very similar to L. andersonii, and those vouchers may be misdetermined L. andersonii.
L. torreyi is supposed to have woolly-ciliate corolla lobe margins, whereas L. andersonii has glabrous to finely straight-ciliate margins. There is also a large difference in the ratio of the corolla lobes to corolla tube. On 4/6/11 I measured the ratio of a number of flowers from plants in the Indian Canyons west of Palm Springs. All were consistent only with L. andersonii, despite some having ciliate corolla lobe margins.
There is also supposed to be a difference in the ratio of the calyx lobes to calyx tube, but this measurement is fraught with peril because exactly what is lobe and what is tube depends on the orientation of the calyx. In many Lycium flowers, there is one deep division in most calyces, with all other divisions shorter, so you'd get very different values for the lobes and tube if that deep division was used.
Although I found no plants that could be considered L. torreyi from the Indian Canyons west of Palm Springs, there are two vouchers of L. torreyi from there, and six vouchers of L. andersonii. Hitchcock, who defined the species of L. torreyi, stated
Among the North American species, it would appear that L. Andersoni and L. Torreyi may occasionally hybridize where the ranges of the two species overlap-in the Coachella Valley of southern California and in Arizona and southern Utah. Through-out its range L. Torreyi has white-fringed corolla-lobes, and a more thick, but proportionately shorter, corolla-tube than L. Andersonii, the latter species having but sparsely ciliate corolla-lobes. However, where the two species occur together, forms have been collected having the slender corolla-tube and leaves of L. Andersonii but with the lobes of the corolla being lanate as in L. Torreyi, the habit of the plant being more like that of L. Torreyi. Similarly, at least one instance has been noted where L. Richii [TJC: =L. brevipes] has apparently hybridized with L. Torreyi; this plant was collected in the Coachella Valley, the only region where the two species overlap in range.
It may be that Hitchcock's "L. torreyi" from the Coachella Valley may be due to a looser interpretation of how woolly-ciliate the corolla lobe margins need to be to qualify a specimen as L. torreyi. It would be good to re-examine those vouchers using the current determination of woolly vs. straight-ciliate. Many "hybrids" of the past have gone away once the full range of variation within a species has been recognized.
Things to Add to This Page in the Future
Need to update page to discuss heterostyly, and thus how one can be confused about the "corolla lobes 1/3 tube" depending on what type of flower is present.
- lycium DO produce at least two, and maybe three, types of flowers. this is called "heterostyly", and has evolved to prevent self-pollination. - flowers with short stamens and long pistils are called "pin" flowers - flowers with long stamens and short pistils are called "thrum" flowers. the styles in "pin" flowers are shaped like "pins", hence the name. i couldn't find the origin of the name "thrum". - "Species of Lycium seem to present various degrees of dioecy and sometimes have quite different forms of flowers on different plants (e.g., pin and thrum flowers on different individuals in L. exsertum and L. fremontii; Miller & Venable 2000)"