Plant Species of San Jacinto Mountain:
Pterospora andromedea, pinedrops
Growth Rate and Bloom Time
Fig. 1. Growth sequence of pinedrops (left to right in top row, then left to right in bottom row) from its emergence from the ground (top left) to one year old dried fruit (bottom right). The figure looks best if your browser is at least 850 pixels wide so the pix are side by side in two rows. Click on the pictures for larger versions.
Fig. 2. Two different individual flowers of pinedrops, seen from the side and from below, and a fruit. The figure looks best if your browser is at least 850 pixels wide so the pix are side by side in two rows. Click on the pictures for larger versions.
Pterospora andromedea, pinedrops or pine drops, is a lovely tall mycotrophic ("fungus feeding") plant that has no leaves and no chlorophyll, only flowers that have small bracts. It has no ability to make food on its own, and takes all of its nutrition from the fungus on which it is a parasite. The flowers of pinedrops, and its close relatives, emerge from the ground without leaves and without any green coloring typical of plants. They are sometimes called "fungus flowers", since they can look like the fruiting bodies of fungus when they first emerge from the ground.
Pinedrops is one of the later bloomers at San Jacinto Mountain, with plants emerging from the ground in July, and blooming in late July and August. The dead stalks persist for at least a year, and perhaps for multiple years.
Pinedrops take advantage of the "wood wide web" of ectomycorrhizal fungi that build vast underground networks to gather nutrients. These fungi are in a symbiotic relationship with the trees whose roots they tap into, absorbing carbohydrates and other nutrients from the trees, and in turn supply the trees with water and minerals. However, at least according to our current understanding, mycotrophic plants are parasitic on the fungi, stealing everything they need to grow from the fungi, and giving nothing back to the fungi in return. See What are Mycotrophic Wildflowers? from the U.S. Forest Service for more information.
The pine in the common name pinedrops recognizes that there are pine trees, with their associated ectomycorrhizal fungi, in the areas where pinedrops grows. The drops are the individual flowers, which are pointed downward, as if they were "dripping" from the flowering stem.
The genus name comes from the Greek pteros, "a wing," and spora, "seed," thus "winged seed". And what a heck of a wing the seed has! The wing is 10 times longer than the seed; see this picture from botany.org showing the small red seed and the large translucent wing. This large wing, with the lightweight seed, allows the seed to be spread by the wind. There is only a single species in this genus; the specific epithet andromedea refers to the related genus Andromeda; see the original publication of the name by Thomas Nuttall in 1818, where he compares the structure of the base of the anther to it.
Most people are very surprised to learn that pinedrops are in the heath family, Ericaceae, along with rhododendrons and manzanitas! This isn't some recent result of molecular work; this grouping was recognized in the 1800s, and so far has been confirmed by molecular work. The flowers of pinedrops are very similar to the flowers of manzanitas in shape, so at least those two members of the family have that in common.
The heath family is divided into something like nine subfamilies, with the mycotrophic plants in one of them.
Pinedrops are somewhat similar to snowplant, and photographs of the two in fruit at iNaturalist are sometimes mistaken for each other; see, for example, this one. In the field, there usually is no doubt about the determination. Snowplant emerges much earlier in the year, is a brilliant red color, has much denser flowers and fruit on a fatter stem, with flowers that are horizontal, not drooping, and is in fruit before pinedrops even emerge.
Although it is said to be a perennial in the Jepson Manual treatment, pinedrops acts very oddly for a perennial, since it has a peculiar habit of popping up in different places in some years. Dave reported that he would never know where it would appear in his Pine Cove yard each year; only rarely would new stalks appear in the same place where there had been old stalks. Most of the time when we see fresh stalks at San Jacinto Mountain, there are no old stalks in the same area. But sometimes there are! It was called an annual in the original publication, and "annual or perennial" in the 1959 monograph by Bakshi.
Fig. 3 shows the geographic distribution of 61 locations of Pterospora andromedea from our digitized surveys.
Fig. 3. The 61 locations where we have observed Pterospora andromedea from our digitized surveys as of 11 August 2019. The digitization is complete only above 9000 feet elevation, and becomes progressively more incomplete at lower elevations. Click on the map for a larger version.
Fig. 4 shows a histogram of the elevations for our observations of this species. For comparison, Munz 1974 gives the elevation range for this species in southern California as 5000 to 9000 feet, very similar to what we have observed.
Fig. 4. A histogram of the elevations where we have observed Pterospora andromedea from our digitized surveys as of 11 August 2019.
Pinedrops is widespread in North America. It occurs in every state west of the Great Plains, as well as in the northernmost part of eastern North America; see BONAP's North American Plant Atlas geographic map for it. It is also present in Mexico.
Growth Rate and Bloom Time
Tom serendipously took a series of photographs of a group of three flowering stalks growing on the Devils Slide Trail in 2019 on five separate hikes, on 15, 22, 26 July, and 1 and 8 August. These plants were originally discovered by Nancy Accola. On 1 August Tom measured the spacing of the plants, and the height of the tallest plant, which then allowed measurements of the height of all three plants on all five dates from the photographs, shown in Fig. 5.
Fig. 5. Growth rate of three plants of Pterospora andromedea from the Devils Slide Trail.
As shown in Fig. 5, the growth rate is remarkably uniform, with every single measurement falling on the line fit to the data until the plant reaches its final length. The only odd point is the 8/1/19 measurement for plant 3, which is taller than expected. Tom went back and measured three different photographs on 8/1/19, with the same results. There was one perhaps significant difference in the photographs for 8/1/19; Tom photographed the plants in the evening, on his way down the Devils Slide Trail, whereas all the other photographs were taken around noon on his way up. It is also possible there was just something different about the way plant 3 terminated its flowering stem than the way the other plants did so.
The growth rate of the three plants was 2.8, 2.4 and 2.3 cm per day (1.10, 0.95, and 0.90 inches per day), for plants 1, 2 and 3, respectively. Using the fitted line, the emergence from the ground of the three plants was 4, 8 and 11 July, with the plants reaching their full height on 4 and 2 August for plants 1 and 2. Since the measurement for plant 3 just before its maximum height does not fit the line well, it is a bit unclear exactly when it reached its full height, but it was somewhere between 1 and 6 August.
Tom observed the first flower of Plant 1, the tallest plant, on 27 July and its last few flowers on 8 August 2019, which probably lasted a few days more. Thus plant 1 grew for 31 days; began flowering 23 days after it emerged from the ground; and its flowering period lasted a minimum of 9 days, and probably around 11 days.
The individual photographs of this set of three flowering stalks are displayed in Fig. 6, all at the same scale for the distance between the plant on the left and the closest of the other two plants. The camera location is not exactly the same in all photographs, since I didn't realize I might be using these photographs in the future.
15 July 2019
22 July 2019
26 July 2019
1 August 2019
8 August 2019
Fig. 6. Repeat photographs of the same group of pinedrops over a period of 24 days. Click on the pictures for larger versions.
Copyright © 2019 by Tom Chester and Dave Stith.
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Updated 23 August 2019.