Plant Species of the South Kaibab Trail:
Eastwood's sandwort, Arenaria eastwoodiae

See Plant Guide to South Kaibab Trail for an introduction to this page, especially the Introduction To These Species Pages.

The Flora of North America calls this taxon Eremogone eastwoodiae.

Characteristics

Identification status: High confidence. No other species at the Grand Canyon fits.

When I first saw this, I couldn't even figure out the family, even though I should have from the single flower we saw. I had forgotten my own rule: if you can't figure out what family a plant is with regular flowers, try Caryophyllaceae. (:-)

McDougall family key:

1'   Non-woody plants
87'  Plants with green color in leaves
92'  Not a cactus
93'  Not a grass or rush
96'  Not an Asteraceae
97'  Plant growing in dry places
102' Flower parts in 5's
106' Corolla present
125  Petals distinct
126' Ovary superior
130' Flowers regular
134' Stems not prostrate
135' Sepals 5
137  Leaves opposite
138' Flowers not yellow
140  Styles 3, distinct  .... Caryophyllaceae

1'   Sepals distinct
6'   Styles 3
8    Petals entire
9'   Leaves linear or awl-shaped, rigid and sharp-pointed
10'  Sepals sharp-pointed

11   Petals conspicuously longer than the sepals ... A. macradenia
11'  Petals not conspicuously longer than sepals

12   Plants bluish-green; leaves only moderately rigid and sharply pointed ...A. fendleri
12'  Plants light green or yellowish; leaves very rigid and sharply pointed ...A. eastwoodiae

The definitive keying stopped after key element 10', so I presented all the couplet elements after that.

Specifically, in couplet 11 it is unclear exactly what Petals conspicuously longer than the sepals means. Worse, according to the Flora of North America treatment, A. macradenia (=Eremogone macradenia) can have petals only as long as the sepals, so this couplet is not accurate in general, although it might (or might not) be correct for the Grand Canyon plants.

In couplet 12, the color of plants is notoriously difficult to determine, because people see colors in different ways, and dried plants sometimes change color from live plants. It is also unclear exactly what moderately rigid is compared to very rigid; this also might change upon drying. Key couplets like this one are meant to be used in a dried specimen in a herbarium, where one can have several examples of each species side by side and match a specimen to known examples of the two species. In the field, it is very difficult to use such couplets unless one is already familiar with both species.

This leaves three species in play: A. macradenia, A. fendleri, and A. eastwoodiae.

Here are some characteristics measured from the photographs below to try to discriminate between these three species. I've used my thumbnail for scale for the flower and capsule, and then used the capsule to estimate the leaf and stem lengths. The latter resulting estimate of course is terribly uncertain, but still gives decent results to the order of 50% or better. I couldn't easily put a scale in my picture of the entire plant since the plant was on a ledge above the trail.

The above rules out A. macradenia, that, according to the Flora of North America treatment, has stems 20-40 cm, leaves 2-6 cm, sepals 4.5-7.2 mm, petals 6-11 mm, and the capsule 6-8 mm.

A. fendleri is ruled out on that plant being glandular (see these pictures) and having capsules 5-7 mm. (See its Flora of North America treatment.)

Fortunately, the third possibility, A. eastwoodiae, fits fairly well; see its Flora of North America treatment. The plants below match the SEINet voucher picture, and they fit the Flora of North America description with only the sepals and petals being slightly shorter than the values of (3.5-)4-6.5 mm and 4-6.5 mm, respectively. However, those two quantities fit this species better than they fit the other two species, and we observed the very last flower of the season, which often tends to be smaller than typical flowers. The capsule length of ~3.8 mm fits the 4-6 mm length of this species well.

Jan Busco kindly confirmed this determination, and added some useful information on discriminating A. eastwoodiae from A. fendleri:

As a field characteristic, the leaves of A. eastwoodiae are sharp to the touch and to the eye, while those of A. fendleri are not. Also, in northern Arizona, A. fendleri is frequently more of a meadow/grassland plant and A. eastwoodii occurs in harsher, frequently dryer or locations.


From a SEINet search on 4 September 2008, there are 16 vouchers of this species from the Coconino County portion of the Grand Canyon. The nearest are at: Near El Tovar; and Grandview. Note that there may be additional vouchers at other herbaria not available through SEINet.

First occurrence on South Kaibab Trail: mile 0.05, elevation ~7180 feet (~2190 m).

Number of plants along Trail: at least 10 plants were found in at least different 3 locations in August 2008. However, flowers were not present on the other specimens, so there is no guarantee those at other locations are this same species.

Pictures

From 23 August 2008, mile 0.05:

References


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Copyright © 2008 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
http://tchester.org/gc/plants/species/arenaria_eastwoodiae.html
Comments and feedback: Tom Chester
Last Update: 5 September 2008