Plant Species of San Jacinto Mountain: Carex senta and C. schottii
Table of Contents
Introduction
Measurements of Some Carex senta Plants From the Field
Measurements of Carex senta From Floras
Keys to Distinguish C. senta from C. schottii
Comparison of Field Measurements with Floras
Comparison of Field Measurements of C. schottii and C. senta
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| Fig. 1. Photographs of the first C. senta plant measured in the field, Plant #1 in Table 1.
Top: Two inflorescences. The left top pix shows a wide (~ 5 mm) infl bract that exceeds the top of the infl. The infl has one terminal male spikelet, a second spikelet that is entirely male except for a few female fruit at the bottom, and three female spikelets. The right top pix shows a narrow infl bract (~ 2 mm) that is shorter than the top of the infl. The infl has a terminal male spikelet, a second spikelet that is half male, half female, and three female spikelets. Bottom: pix of the entire plant, with at least eight inflorescences visible, with Patrick Drew on its upper left for scale. | |
Introduction
This page currently has a historical organization, with its first purpose to make sure of the determination of our high elevation plants called Carex senta. The work reported here definitively established that the plants above 7500 feet elevation in the Tahquitz Valley area were C. senta, and not C. schottii.
Subsequently, I came across plants of C. schottii at lower elevations on the Sawmill Flats Road, and then at Lake Fulmor and the James Reserve at Hall Canyon. I measured them for two key characteristics that discriminate the two species.
If you just want to see how reliably one can distinguish Carex schottii from C. senta at San Jacinto Mountain, jump to Fig. 2 in the last section,
Comparison of Field Measurements of C. schottii and C. senta, which reports those measurements.
This page was stimulated by Keir Morse, who observed plants in the San Bernardino Mountains that keyed to Carex schottii using the Jepson eFlora key. Those plants formed large clumps similar to those of our C. senta plants in the San Jacinto Mountains. The Jepson eFlora key distinguishes those two species by C. schottii being "cespitose", and C. senta being rhizomed. The obvious inference from this key is that C. senta shouldn't form big clumps. But it does!
Calling some Carex cespitose and others rhizomed is more than a little confusing, since all Carex have rhizomes. The Flora of Arizona Carex treatment by Rink and Licher has the clearest statement on the distinction:
Rhizomes vary from short to long-creeping. The short- rhizomatous species are cespitose (clump-forming) and those with long-creeping rhizomes are colonial or turf-forming. ... Cespitose species often have stems so close together that the rhizomes are indiscernible. Some species with longer rhizomes still grow in clumps, with the rhizomes crossing each other in an interwoven mass. Other species with longer rhizomes grow in small clumps (3-6 culms), but can have long rhizomes between clumps.
After much email discussion between Keir and me, consultation of a number of floras that didn't always agree with each other, and some analysis of iNat posts, it became clear that it was necessary to understand how variable each of these two species were individually before one could hope to try to distinguish the two reliably. Hence on 21 August 2024 I measured two San Jacinto plants of C. senta to at least start to see the range of their characteristics.
With the help of Patrick Drew, I measured the first two plants we came across, in different areas around Skunk Cabbage Meadow. This page was begun simply to report those measurements, and compare them to measurements given in the floras and in keys to distinguish C. schottii and C. senta.
Patrick and I measured two additional C. senta smaller plants on 26 August 2024. For comparison, Keir measured two plants in the San Bernardino Mountains, one plant of C. senta and one plant of C. schottii, on 27 August 2024.
Subsequently, I came
Measurements of some Carex senta plants From the Field, and One C. schottii
Table 1. Measurements of Some Carex senta Plants From the Field, and One C. schottii
| Characteristic | Plant #1 | Plant #2 | Plant #3 | Plant #4 | SnBr Keir | SnBr Keir C. schottii | |
|---|---|---|---|---|---|---|---|
| Height (cm) | 122 | 102 | 132 | 82 | 120 | 166 | |
| Width (cm) | 201 | 180 | 98 | 95 | 140 | 250 | |
| Leaf length min (cm) | 56 | 84 | 23 | 20 | |||
| leaf length max (cm) | 86 | 117 | 80 | 74 | 75 | 104 | |
| leaf width min (mm) | 6 | 4 | 4.5 | 4.5 | 4 | 4 | |
| leaf width max (mm) | 8 | 7 | 5.5 | 7 | 7 | 11 | |
| Rhizome spacing min (cm) | 1 | 1 | 1.5 | 1.5 | 1 | 1 | |
| Rhizome spacing max (cm) | 6 | 3 | 3 | 4 | 5 | 5 | |
| Infl stem length min (cm) | 107 | 99 | 98 | 69 | 71 | 98 | |
| Infl stem length max (cm) | 124 | 107 | 98 | 84 | 109 | 144 | |
| Infl length min (cm) | 12 | 10 | 7 | 8 | 4.5 | 8.5 | |
| Infl length max (cm) | 23 | 12 | 12.5 | 9 | 12 | 27 | |
| Infl bract length min (cm) | 19 | 9 | 7.5 | 6 | 8.1 | 3.5 | |
| Infl bract length max (cm) | 22 | 15.5 | 10.5 | 8 | 10 | 13.9 | |
| Infl bract width min (mm) | 2 | 2.5 | 3 | 1 | 3 | 3 | |
| Infl bract width max (mm) | 5 | 4 | 3.5 | 1 | 4 | 5 | |
| # male spikes min | 1 | 1 | 2 | 1 | 1 | 2 | |
| # male spikes max | 2 | 2 | 2 | 1 | 3 | 3 | |
| # female spikes min | 3 | 3 | 2 | 3 | 2 | 1 | |
| # female spikes max | 3 | 4 | 4 | 4 | 4 | 3 | |
| Terminal spike length min (mm) | 28 | 30 | 25 | 25 | 12 | 28 | |
| Terminal spike length max (mm) | 37 | 45 | 40 | 30 | 26 | 35 | |
| Terminal spike width min (mm) | 3.5 | 4 | |||||
| Terminal spike width max (mm) | 4 | 6 | |||||
| Pistillate spike lengths min (cm) | 30 | 40 | 20 | 13 | 8 | 24 | |
| Pistillate spike lengths max (cm) | 50 | 53 | 52 | 43 | 39 | 84 | |
| Pistillate spike width min (mm) | 3.5 | 4 | 4 | 4 | 4 | 6 | |
| Pistillate spike width max (mm) | 5 | 5 | 5 | 6 | 5 | 7 | |
| Infl bract / infl | <1 to >1 | <1 to >1 | +- equal to somewhat less | +- equal to << 1 | |||
| Stoloniferous | no | no | no | no | no | no | |
| Clumping | large clump | small clump | linear clump | linear clump | loosely cespitose | dense tussock | |
| Clump size at base of stems (cm) | 34 | 18 | 8.5 | 21 | |||
| # stems in clump | 110 | 19 | 26 | 16 | |||
| Spacing between clumps min (cm) | 6 | 12 | |||||
| Spacing between clumps max (cm) | 12 | 18 |
Plant #1 is shown in Fig. 1; in my iNat observation; and in Patrick Drew's iNat observation. This plant is growing in a drainage feeding into upper Skunk Cabbage Meadow, right next to the water flowing there on 21 August 2024. This drainage usually has flowing water in early summer except in very dry years.
In addition, Patrick and I measured a larger plant right next to the first plant. It was 112 cm high, and 315 cm wide.
Plant #2 is shown in my iNat observation. This plant is growing in a small drainage just northeast of Skunk Cabbage Meadow that flows into Candy's Creek a short distance below the bottom of Skunk Cabbage Meadow.
Plant #3 is shown in my iNat observation. This plant is growing in the seep area of the uppermost Powderbox Spring Drainage on the Devils Slide Trail. There is only a small patch of Carex senta here, with sharp demarcations between this patch and its neighbors. This area used to be much wetter 25 years ago. It dried considerably in the drought years of 2001 and following. This is the driest general area in which I remember seeing Carex senta, except at the edges of meadows.
Plant #4 is shown in my iNat observation. This plant is growing at the extreme dry edge of Skunk Cabbage Meadow.
Some entries in Table 1 are blank since we didn't measure every characteristic on each day.
Some details on the measured quantities:
Height. The farthest part of the plant above the ground, which could be the longest culm, or the highest part of the leaves as they bend back toward the edge of the plant.
Width. The full horizontal extent of the plant, from the in-situ ends of the leaves on one side of the plant to the ends of the leaves on the other side.
Rhizome spacing. The distance between the base of the stems. This is a somewhat ill-defined measurement since we don't know how the base of the stems are connected by rhizomes, especially if there are overlapping rhizomes present.
Infl stem length. The full length of a flowering culm, from the ground to the tip of the terminal spike.
Infl bract. The leaf-like bract at the lowest node of the inflorescence.
Infl length. The length of the flowering part of the culm, from the node at the base of the first infl bract and the base, or stalk, of the proximal spikelet.
Infl bract / infl. The relative length of the top of the infl bract and the top of the terminal spike in the infl. A value of 1 means that they both reached the same height. A value < 1 means that the bract tip is below the top of the terminal spike, as shown in the top right pix in Fig. 1. A value > 1 means that the bract tip reaches beyond the top of the terminal spike, as shown in the top left pix in Fig. 1.
# male and female spikelets. A spikelet with mixed male and female flowers was counted only once, under whatever sex was dominant in the spike. There were no spikelets that were half male and half female. Male spikelets were either all male, or had just a few female flowers at their base. Female spikelets were either all female, or had significantly fewer male flowers at their tip than the number of female flowers.
Clump size at base of stems. This is often ill-defined, since it is not always apparent where one clump ends and another begins.
Measurements of Carex senta Given In Floras
Table 2. Measurements of Carex senta From Floras
| GPS # | Mackenzie 1922 | Jepson 1925 (by Mackenzie) | Abrams (by Mackenzie) 1955 | Mason 1957 | Munz 1974 | JM 1993 Mastrogiuseppe | Yosemite Flora Botti 2001 | FNA Ball and Reznicek 2002 | JM 2 2012 (also Rev. 3 2015) Zika, Hipp, and Mastrogiuseppe | Prigge & Gibson SMM 2013 | Flora of Arizona 2015 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Height (cm) | 30-90+ cm | ||||||||||
| Width (cm) | Often taller than wide | ||||||||||
| Leaf length min (cm) | |||||||||||
| leaf length max (cm) | < culm length | 41 | |||||||||
| leaf width min (mm) | 3 | 3 | 3 | 2 | 3 | 3 | 3 | 4 | 3 | 3 | 1 |
| leaf width max (mm) | 5 | 5 | 5 | 6 | 5 | 5 | 5 | 8 | 5 | 5 | 6 (8) |
| Rhizome spacing min (cm) | |||||||||||
| Rhizome spacing max (cm) | |||||||||||
| Infl stem length min (cm) | 40 | 40 | 40 | 30 | 30 | 40 | 50 | 40 | |||
| Infl stem length max (cm) | 90 | 90 | 70 | 100 | 100 | 70 | 100 | 80 (100) | |||
| Infl length min (cm) | (5)7 | ||||||||||
| Infl length max (cm) | 15 (19) | ||||||||||
| Infl bract length min (cm) | |||||||||||
| Infl bract length max (cm) | |||||||||||
| Infl bract width min (mm) | 3 | ||||||||||
| Infl bract width max (mm) | 5 | ||||||||||
| # male spikes min | 2 | 1 | 1 | 2 | 2 | 1 | |||||
| # male spikes max | 3 | 2 | 1 | 3 | 3 | 3 | |||||
| # female spikes min | 1 | 1 | 1 | 2 | 1 | 2 | 1 | 2 | |||
| # female spikes max | 3 | 3 | 3 | 3 | 3 | 4 | 3 | 4 | |||
| Terminal spike length min (mm) | 30 | 30 | 30 | 25 | 30 | 15 | |||||
| Terminal spike length max (mm) | 45 | 45 | 45 | 50 | 45 | 55 | |||||
| Pistillate spike lengths min (cm) | 25 | 25 | 25 | 25 | 30 | 25 | 25 | 30 | 25 | 15 | 20 |
| Pistillate spike lengths max (cm) | 50 | 50 | 50 | 50 | 45 | 50 | 50 | 70 | 50 | 55 | 80 |
| Pistillate spike width min (mm) | 5 | 5 | 5 | 3 | |||||||
| Pistillate spike width max (mm) | 9 | 9 | 5 | 5 (9) | |||||||
| Infl bract / infl | <1 to >1 | <1 to >1 | < 1 to >1 | <1 | <1 to >1 | ||||||
| Stoloniferous | yes | ||||||||||
| Clumping | Loosely cespitose and stoloniferous | Loosely cespitose and stoloniferous | More loosely cespitose than C. schottii, which is “cespitose in large clumps with long rhizomes” | Loosely cespitose and stoloniferous | forming large, dense, raised clumps connected by rhizomes, in +- continuous stands or not | very densely tufted, forming large clumps connected by rhizomes | not cespitose | loosely cespitose or rhizomed | rhizomatous, forming dense clump | loosely to densely cespitose, with stout rhizomes | |
| Notes | terminal spike staminate, with 1-2 smaller ones at base | More info in key, but for C. senta, C. angustata, C. nudata combined | Illustration shows five spikelets; key says infl bract usually >= infl |
I have purposefully left in the blank lines for the min Leaf Length, the min and max rhizome spacing and Infl bract length, so that Table 1 and Table 2 have perfect correspondence for the characteristics, and to make visible what is missing from the floral descriptions.
The floral measurements are presented by the date of the flora, from oldest to most recent.
Keys to Distinguish C. senta from C. schottii
The floral keys below are presented from oldest to most recent floras. Some of the keys have C. schottii and C. senta distinguished in a single couplet. Other keys have them distinguished as part of a group of species, which are given below. I've placed the species, or group of species first, to make it clearer up front which is the case.
Mackenzie 1922; Jepson 1925 (by Mackenzie); Abrams (by Mackenzie) 1955
C. schottii. Lower culm sheaths strongly yellowish-brown tinged, sharply keeled; culms stout, the leaf-blades 6-12 mm. wide
C. senta. Lower culm sheaths purplish-tinged, not sharply keeled; culms more slender, the leaf-blades narrower
Mason 1957
C. schottii. Leaf blades 5-12 mm wide; pistillate spikes 5-20 cm long
C. senta. Leaf blades 2-6 mm wide, pistillate spikes 5 cm long or less
Munz 1974
C. schottii. Leaf sheaths strongly carinate dorsally; blades 6-12 mm broad; culms 10-15 cm tall
C. senta. Leaf sheaths slightly carinate or rounded dorsally; blades 3-5 mm broad; culms 3-10 cm tall
JM 1993 Mastrogiuseppe
C. schottii. Pl 1-1.5 m; lf blade 4-12 mm wide; bladeless sheath > 7 mm wide at midlength, keeled; perigynium (2.7)3-4.5 mm; staminate spikelets 2-7, terminal often > 5 cm; lateral spikelets gen 5-20 cm, 5-7 mm wide, stalks 0 or long, +- nodding; lowest spikelet bract lf-like, gen > infl
C. senta, C. angustata, C. nudata. Pl gen < 1 m; lf blade 2-9 mm wide; bladeless sheath < 7 mm wide at midlength, not keeled; perigynium 2-4 mm; staminate spikelets gen 1-2, terminal < 5 cm; lateral spikelets (1.5)2-9 cm, < 6 mm wide, stalks 0 or erect; lowest spikelet bract lf- or bristle-like, < or > infl
FNA Ball and Reznicek 2002
C. schottii and many others. Proximal bract longer than inflorescence (usually at least 1.5 times as long)
C. senta and many others. Proximal bract shorter than or equal to inflorescence
JM 2 2012 (also Rev. 3 2015) Zika, Hipp, and Mastrogiuseppe
C. schottii and others. Plant cespitose; peri veined
C. senta and others. Plant rhizomed; peri veined or not
Mistretta 2020
C. schottii. Some leaves > 7 mm wide
C. senta. All leaves < 7 mm wide
Comparison of Field Measurements with Floras
The field measurements made on the four San Jacinto Mountain specimens fit C. senta quite well, and fit C. schottii poorly, making the determination of these San Jacinto plants C. senta. The clearest distinctions are on:
Pistillate spike length. Measured 1 to 5 cm. Fits the Mason key for C. senta perfectly, 5 cm long or less, and not the 5-20 cm of C. schottii.
Leaf blade widths. Measured 4 to 8 mm. Fits the Mason key better for C. senta, 2-6 mm, than the 5-12 mm for C. schottii. The FNA gives the leaf width for C. senta as 4 to 8 mm, a perfect match for my measurements. The FNA gives the leaf width of C. schottii as 10 to 15 mm.
Infl bract width. Measured 1 to 5 mm. Fits the FNA description for C. senta, 3 to 5 mm, much better than the 10-12 mm for C. schottii. However, note that Keir measured a C. schottii that also had a width of 3 to 5 mm, so the width reported in the FNA may not be accurate.
Terminal spike length. Measured 1.2 to 4.5 cm. Fits the 1993 JM1 key for C. senta, < 5 cm, better than the "often > 5 cm" for C. schottii.
Infl bract length compared to Infl length. Most of the bracts were slightly shorter to slightly longer than the infl. That fits the FNA key best for C. senta, "bract shorter than or equal to infl", compared to the "longer than infl" for C. schottii.
The above analysis showed that the maximum leaf width and maximum pistillate spike length were two of the best discriminants between the two species, and were very easy to quickly record in the field. I subsequently measured more specimens of C. senta, and when I found C. schottii at San Jacinto Mountain, made a special trip on 16 October 2024 to measure specimens of it in the Lake Fulmor area. I've also measured specimens of both species from Idyllwild Park, where both species grow together, and from the Hurkey Creek Waterfall area, where only C. schottii grows.
Fig. 2 plots the maximum leaf width vs. the maximum pistillate spike length for all measured plants of the two species from San Jacinto Mountain.
Fig. 2. Maximum leaf width on a plant vs. the longest pistillate spike length for one of the culms from a plant, for all measured plants from San Jacinto Mountain. The plot shows a good separation between the two species. The two species at San Jacinto Mountain (SnJt) are each geographically consistent, with considerable geographic separation between them, with the exception of Idyllwild Park, where the two species grow together. The specimen at (80, 6) is from Idyllwild Park, and might be a hybrid between the two species since another culm from a nearby plant in the same population has a pistillate spike of just 30 mm; see pix and details of this specimen in my iNat post of it. All other specimens measured at Idyllwild Park fall fit well with measurements made in populations of a single species. See a plot with all Idyllwild Park specimens labeled with a gray plus sign, with the two culms from the same large clump surrounded with a black diamond
The culm of C. schottii with an anomalously-low value for the maximum pistillate spike, plotted at (30,15), is shown here. This plant is in the midst of the C. schottii population of Hall Canyon, and has the widest leaf width of any measured so far. Hence there is little doubt about its determination. Perhaps growing conditions for it just weren't very good at the time it produced its culm.
Some notes on the measurements:
Keir Morse has measured plants of both species from San Bernardino Mountain, and one C. schottii from the San Gabriel Mountains. Fig. 3 is the same as Fig. 2, but now includes plants measured by Keir.
Fig. 3. Maximum leaf width on a plant vs. the longest pistillate spike length for one of the culms from a plant. This plot includes plants measured by me from San Jacinto Mountain, and plants measured by Keir Morse from the San Bernardino Mountains and one plant from the San Gabriel Mountains (at 83,12). Keir's data from San Bernardino Mountains plants, and one San Gabriel Mountains plant, nicely fills in the gap between my C. schottii 30 mm pistillate spike length and the rest of my C. schottii data. (See also a plot of only Keir's data.)
The maximum leaf width alone does a good job of discriminating the two species, with potential ambiguity only for leaf widths of 8 to 9 mm.
The maximum pistillate spike length discriminates 13 of the 17 C. schottii from C. senta.
Using both the leaf width and pistillate spike characteristics only leaves 3 of the 25 plants of both species potentially ambiguous. At least at San Jacinto Mountain, ambiguous morphological determinations can be resolved by geography.
Voucher determinations may be a bit more ambiguous since it is probably rare that the leaf with the maximum width is included in the voucher. The maximum pistillate spike length in a voucher should do a pretty good job for the voucher determination, since that measurement alone discriminates 13 of the 17 schottii from senta.
Also, Keir has noted that the leaves of his voucher specimens notably shrink in width compared to his measurements on fresh leaves. But if one makes a plot like Fig. 3 for voucher specimens alone, it should only move the dividing line between the species for leaf width.
It would be very interesting to measure some vouchers of both species and make a plot similar to Fig. 3.
It is much harder to accurately determine these species from iNat observations, since in general there is no scale to measure either the max leaf width or the pistillate spikelet length. Keir and I noticed that the lowermost pistillate spikes of C. schottii often appear longer and narrower than the ones of C. senta.
I measured the ratio of the lowermost pistillate spike length to width for iNat obs where we had the correct determinations from field work. For the width, I measured the dense part of the spike, and did not include any bracts that stuck out from the dense part.
Table 3 presents the results in order of that ratio, and includes a link to the iNat observation in which the measurement was made.
| Determination | Ratio |
|---|---|
| Carex senta | 4.5 |
| Carex schottii | 5.5 |
| Carex senta | 5.8 |
| Carex schottii | 6.3 |
| Carex senta | 6.9 |
| Carex senta | 7.5 |
| Carex senta | 8.4 |
| Carex senta | 8.4 |
| Carex senta | 9.1 |
| Carex senta | 9.1 |
| Carex senta | 9.1 |
| Carex schottii | 9.4 |
| Carex senta | 9.6 |
| Carex senta | 10.3 |
| Carex senta | 12.3 |
| Carex schottii | 12.8 |
| Carex schottii | 13.0 |
| Carex senta | 14.4 |
| Carex senta | 14.5 |
| Carex senta | 14.6 |
| Carex schottii | 15.8 |
| Carex schottii | 16.0 |
| Carex schottii | 16.1 |
| Carex schottii | 17.4 |
| Carex schottii | 20.0 |
| Carex schottii | 20.0 |
| Carex schottii | 20.0 |
This ratio is not a reliable way to distinguish the two species, although it does "generally" work. Ratios of ~15.5 or more appear to only be found in plants of C. schottii. Ratios of ~12 and less are predominantly C. senta, with 11 out of the 14 such measurements, 78%, being C. senta. Ratios of 12 to 15.5 are a mix of the two species, 4 plants of C. senta and 2 plants of C. schottii.
I also noticed that C. schottii inflorescences appear to contain more spikes than does C. senta. Table 4 presents some measurements made in the field of the number of staminate spikes, mixed staminate / pistillate spikes, and pistillate spikes, which show that this is also "generally" true, but is not very reliable.
The entries in Table 4 are in ascending order of first the # total spikes; then the # male spikes; and then the # female spikes.
Table 4. Number of Male, Mixed, and Pistillate Spikes
| Determination | # male spikes | # mixed spikes | # female spikes | # total spikes |
|---|---|---|---|---|
| C. senta | 1 | 0 | 2 | 3 |
| C. senta | 1 | 0 | 2 | 3 |
| C. senta | 1 | 1 | 2 | 4 |
| C. senta | 1 | 1 | 2 | 4 |
| C. senta | 1 | 1 | 2 | 4 |
| C. senta | 1 | 1 | 2 | 4 |
| C. senta | 1 | 0 | 3 | 4 |
| C. senta | 1 | 0 | 3 | 4 |
| C. senta | 2 | 2 | 0 | 4 |
| C. senta | 2 | 2 | 0 | 4 |
| C. schottii | 2 | 1 | 1 | 4 |
| C. senta | 2 | 0 | 2 | 4 |
| C. schottii | 2 | 0 | 2 | 4 |
| C. senta | 1 | 0 | 4 | 5 |
| C. senta | 1 | 0 | 4 | 5 |
| C. senta | 2 | 2 | 1 | 5 |
| C. schottii | 2 | 2 | 1 | 5 |
| C. senta | 2 | 1 | 2 | 5 |
| C. senta | 2 | 0 | 3 | 5 |
| C. senta | 2 | 0 | 3 | 5 |
| C. schottii | 2 | 0 | 3 | 5 |
| C. schottii | 2 | 4 | 0 | 6 |
| C. schottii | 2 | 2 | 2 | 6 |
| C. schottii | 2 | 2 | 2 | 6 |
| C. schottii | 2 | 2 | 2 | 6 |
| C. schottii | 2 | 1 | 3 | 6 |
| C. senta | 2 | 0 | 4 | 6 |
| C. schottii | 2 | 0 | 4 | 6 |
| C. schottii | 3 | 3 | 0 | 6 |
| C. senta | 3 | 1 | 2 | 6 |
| C. schottii | 3 | 2 | 2 | 7 |
The data in Table 4 show that only C. senta can have a single male spike, and that C. schottii overall has more total spikes than does C. senta. For inflorescences with six or more total spikes, 80% of them are C. schottii, 8 out of 10. But this is not a reliable distinction, since two inflorescences with six or more total spikes came from C. senta.
I thank Keir Morse for stimulating this work, for discussions about it that led to my field measurements, for supplying the Mackenzie original monograph, and for his field measurements of plants from the San Bernardino Mountains. I thank Scott White for providing the information about C. senta from the Illustrated Flora of Yosemite National Park.