Plant Species of San Jacinto Mountain: Linanthus jaegeri and L. pungens
Table of Contents
Introduction
How to Distinguish the Two Species
Abundance and Geographic Distribution of Each Species
L. jaegeri
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L. pungens
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| Fig. 1. Flowers of our two high-elevation Linanthus species. Top: Linanthus jaegeri, San Jacinto prickly phlox. Bottom: L. pungens, granite prickly phlox. Click on the pictures for larger versions. |
Introduction
At elevations above 7000 feet at San Jacinto Mountain, we have only two Linanthus species, L. jaegeri, San Jacinto prickly phlox, found at 7600 to 9700 feet, and L. pungens, granite prickly phlox, found at 7000 to 9500 feet; see Fig. 1. These are both members of what Hall called his crest formation, the species that grow on peaks and ridges above 7000 feet elevation.
Both of these species were previously placed in the Leptodactylon genus, but molecular work has shown that Leptodactylon is part of Linanthus, making the name Leptodactylon defunct. Even earlier, these species were placed in the Gilia genus.
Hall was the first one to see plants that are now called L. jaegeri, which he vouchered in 1901, but he called them Gilia pungens, even though he reported that the flowers all were abnormal in having 6 calyx-teeth, 6 corolla lobes, 6 stamens, and 4-celled ovary.
L. jaegeri was first recognized as a new species in 1932 by Munz, under the name Gilia jaegeri, with its distinct characteristics said to be its flattened leaves and low stature. The type specimen is from Jaeger from Tahquitz Peak in 1921, and the specific epithet jaegeri honors Jaeger. No mention was made of its 5 to 6 lobed flowers! That characteristic may have been rediscovered by Wherry in 1945, since Munz 1959 mentions the number of lobes and gives Wherry as the reference for his treatment.
L. pungens was recognized much earlier, in 1830.
L. jaegeri is one of the 11 or 12 species that only grow at San Jacinto Mountain, being found no place else in the world. In comparison, L. pungens is a very widespread species, found throughout central western North America.
L. jaegeri is a very rare species. There are only nine voucher collection events, all from just three or possibly four locations (voucher locations are often vague). We have found it in only ~20 locations in our surveys, and no one has posted observations of it at iNat that are not one of our 12 locations. This species is nowhere very abundant, and we have seen fewer than 100 to 200 plants total. However, because L. jaegeri grows in very inaccessible habitats, there could be, and likely is, a much larger population in areas essentially impossible to survey except by drone or helicopter.
These two species are rarely found together, since they mostly grow in different habitats:
- L. jaegeri grows most often in forbidding areas of exposed rock slabs, typically on north-facing slopes, but can be found on west- and east-facing slopes as well at its upper range of elevation. It often grows alone.
- L. pungens can also grow in such forbidding areas, generally on sunny south-facing slopes, but also on west- and east-facing slopes. It also grows in less-forbidding sunny rocky south-facing slopes, often with other sun-loving species.
See Fig. 2 for some of their habitats.
| L. jaegeri | L. pungens |
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| Fig. 2. Left: Two habitats of Linanthus jaegeri. Right: Two habitats of L. pungens. Click on the pictures for larger versions. | |
How to Distinguish the Two Species
Number of corolla lobes. Most of the time when there are more than a few flowers on a plant, it is very easy to distinguish these two species: L. jaegeri predominantly has flowers with six corolla lobes, and L. pungens predominantly has flowers with five corolla lobes; see Fig. 1.
However, if there are only a few flowers on a plant, this may not be 100% reliable, since plants in the Phlox family exhibit significant variation in their petal lobe number. The main source of confusion is that L. jaegeri not infrequently has only five petal lobes. Although L. pungens can produce flowers with six petal lobes, that is extremely rare.
Plants of L. jaegeri seen only in the distance can sometimes appear to have mostly five petal lobes, even when there are many flowers with six petal lobes, due to one lobe being not easily visible. See the discussion in this iNat post that stimulated this webpage.
The shape of the corolla lobes is somewhat different, with some lobes of L. pungens wider relative to their length than some lobes of L. jaegeri. The Jepson description says the lobes of L. jaegeri are oblanceolate, and the lobes of L. pungens are obovate. Fig. 1 shows that this distinction is generally true, but the corolla lobes of each species often vary within a single flower from oblanceolate to obovate. It is therefore important to look at a number of corolla lobes to assess their average shape.
Leaves opposite or alternate. Perhaps the easiest discriminant for plants with few or no flowers is that the leaves are alternate for L. pungens, and opposite for L. jaegeri; see Fig. 3.
L. jaegeri
| L. pungens
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| Fig. 3. Photographs showing the opposite leaves of Linanthus jaegeri (left) and the alternate leaves of L. pungens (right). See also the same photographs where some of the leaves are outlined in red for L. jaegeri and L. pungens. | |
However, this isn't as easy as it sounds whenever the growth along the stem is so compact that it is hard to clearly see the leaves. Furthermore, it is often a prickly business to try to use your hands to spread apart the growth to see the leaves more clearly. The specific epithet "pungens" means spiny, sharp-pointed!
Most of the time, the alternate leaves of L. pungens are obvious, as shown in Fig. 3. In contrast, it often is nearly impossible to recognize the opposite leaves of L. jaegeri without very careful study of the leaves, since the plant grows so compactly. See this iNat post of L. jaegeri for some good pix of its opposite leaves from a detached sample of the stem.
Number of leaf lobes. L. jaegeri always has three leaf lobes, and our plants of L. pungens have typically five to seven leaf lobes, although infrequently they have only three leaf lobes; see Fig. 4 and these posts for L. jaegeri and L. pungens.
Also, the lobes of L. jaegeri are said to be pinnate, since the lobes do not arise from the very base of the leaf (yes, this distinction is pretty subtle!). The lobes of L. pungens are palmate, spreading out from the base of the leaf like the fingers from the palm of our hands.
L. jaegeri
| L. pungens
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| Fig. 4. Photographs showing the 3 lobed leaf of Linanthus jaegeri (left) and a 7 lobed leaf of L. pungens (right). The lower side of the leaf is shown for L. jaegeri and the top side of the leaf for L. pungens, so ignore the difference in appearance other than the number of lobes.. | |
This can often be seen by close inspection of the leaves in the field without removing a leaf.
The color of the flowers. Although color is often tricky to use in the field, since lighting conditions vary so much, we have been successful in the past in recognizing both species from some distance just by using the color of the flowers. The flowers of L. jaegeri range from a rich white to a rich creamy white. The flowers of L. pungens are a "thinner" color, and range from white to pink. See Fig. 1 for the difference in color; note that both color variations of L. jaegeri are apparent, depending on how open the flowers are. Fully open flowers are a rich white, and partially open flowers, for this plant, show a rich creamy white.
Until you have significant experience in seeing both species, probably the only reliable use of this difference is if you see flowers with any touch of pink, which nails them as L. pungens.
Hairs on the stem, leaves, and calyx. L. jaegeri only has glandular hairs, whereas our plants of L. pungens have both glandular and non-glandular, somewhat-cobwebby hairs. This discriminant probably is only useful for botanists accustomed to looking at minute hairs on a plant with a hand lens. (Pix to be added).
Fruit capsule. The fruit capsule of L. jaegeri generally is 4 valved, whereas the fruit capsule of L. pungens is generally 3 valved. This is probably directly related to the number of corolla lobes.
Size of the plant. L. jaegeri is on average a smaller, more compact plant than L. pungens. This distinction is used in the Munz key to separate the species. Munz says that L. jaegeri is 2 to 10 cm (1 to 4 inches) high, and that L. pungens is 10 to 40 cm (4 to 16 inches) high.
To see how well the size of the plant separates the species, I measured all the accessible specimens of L. jaegeri on the Devils Slide Trail on 5 July 2022 (see pictures of them with their measurements), and a roughly equal number of specimens of L. pungens from the same trail on the same day (see these three iNat obs with their measurements). All specimens had produced flowers. Fig. 5 shows that size is a fairly good discriminant for the majority of plants, but that some plants of both species can be the same size. Heights less than 7 cm are exclusively L. jaegeri, and height greater than 12 cm are exclusively L. pungens. Plant diameters less then 15 cm are exclusively L. jaegeri, and diameters greater than 30 cm are exclusively L. pungens.
Fig. 5. Plant height vs. plant maximum diameter for both species.
Abundance and Geographic Distribution of Each Species
L. jaegeri grows in such forbidding habitats that Hall only found it in two places in his 1902 Flora of the higher elevations of San Jacinto Mountain: one small clump on the very summit of Tahquitz Peak, altitude 8800 ft., and in cracks of rocks at about the same altitude on a ridge near Lake Surprise. In contrast, he found L. pungens being well-distributed along all the ridges of the Upper Transition Zone.
In the 120 years since Hall found it in two places, there was only one, or perhaps two, additional locations from other from vouchers. We have found it in only ~20 locations in our surveys, and no one has posted observations of it at iNat that are not one of our 12 locations.
Fig. 6 uses only the results from our digitized surveys to show the locations at which we have seen these species. We have at least two additional locations for L. jaegeri from data that have not yet been digitized.
L. jaegeri
| L. pungens
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| Fig. 6. The geographic distribution of L. jaegeri (left) and L. pungens (right). | |
Nearly all locations of L. jaegeri are on north-facing exposed rock slabs, whereas L. pungens is found in a wider variety of habitats
We thank the UCR California Naturalist Group that Tom met on the trail on 24 June 2022 for stimulating this page after they noticed a plant that appeared to have mostly 5 lobed flowers when observed from a distance. We also thank Deb Nelson for help with fieldwork on 30 June 2022 to work on using the leaf lobes and trichomes to discriminate these two species.