Plant Species of the South Kaibab Trail:
small-seeded spurge, Chamaesyce polycarpa

Synonym: Euphorbia polycarpa.

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

Characteristics

Identification status: Due to their fused lower stipules, these plants seem to fit only Chamaesyce polycarpa. But C. fendleri is apparently the most common species here, so it would be good to measure the size of the fruit and seeds, and to make sure that some specimens of C. fendleri in Arizona don't have fused lower stipules. Also, I don't have any information about C. chaetocalyx = C. fendleri var. chaetocalyx, other than a single online picture of that taxon, which shows much narrower leaves than the specimens here.

These plants in fact key to C. fendleri using the McDougall key, since he assumes that all plants of Chamaesyce polycarpa are actually var. hirtella, the hairy version of C. polycarpa:

1' Non-woody plants
2' Sepals and petals lacking; flowers with a calyx-like involucre with 1 female
   flower at center surrounded by several male flowers, resembling a perfect flower
3' Glands on the margins of the involucre with petal-like appendages

6  Stems, leaves, ovary and fruit somewhat hairy ... C. polycarpa
6' Stems, leaves, ovary and fruit not hairy ... (7)

7' Leaves not linear
8  Plant perennial; leaves broadly ovate ... C. fendleri

Since these plants are dead glabrous, McDougall would key them to C. fendleri. (McDougall uses the genus Euphorbia instead of Chamaescye.)

However, the Grand Canyon Flora has both the glabrous C. polycarpa and its hairy var. hirtella in it, so the key above is incomplete. There is no key that I can find to separate C. polycarpa and C. hirtella specifically for Arizona plants, but the Jepson Manual for California differentiates them as follows:

17  Fruit longer than 2 mm; stipules separate; seed longer than 2 mm ........C. fendleri
17' Fruit shorter than 2 mm; lower stipules fused; seed shorter than 2 mm ...C. polycarpa

I didn't measure any fruit or seeds, but there is no doubt that the lower stipules are fused, making these plants C. polycarpa, assuming that differentiating characteristic can be trusted in Arizona. A picture of one voucher from Arizona does show separate lower stipules.

Other differences from the Jepson Manual description are:

CharacterC. fendleriC. polycarpa
Leaf shapeovateround to ovate
Leaf tipacuteobtuse
Stipulelineartriangular
Gland appendagenarrower than gland, scalloped, whitenarrower to wider than gland, entire to scalloped, white to red
Fruit length2.0-2.5 mm1.0-1.5 mm

The leaf shape is ovate, which could fit either. The leaf tip is acute to obtuse, which doesn't fit either species alone. The upper stipules are linear to triangular, which also doesn't fit either species alone. The gland appendage is white to pink, and is as wide to wider than the gland, both of which fit only C. polycarpa. The appendage is scalloped, which fits either species.

Summary: 3 characteristics fit only C. polycarpa, including one key characteristic; zero characteristics fit only C. fendleri, and two characteristics have the simultaneous characteristics of both species, and thus don't fit either species exactly.

A determination of C. polycarpa hence seems quite likely, but I'd only feel secure in this id after measuring some fruit, and after knowing more about C. chaetocalyx.


From a SEINet search on 6 September 2008, there are just 3 vouchers of this species from the Coconino County portion of the Grand Canyon. The nearest is at Bright Angel Trail near the Colorado River (var. hirtella). Note that there may be additional vouchers at other herbaria not available through SEINet.

In contrast, there are 13 vouchers of C. fendleri, including var. chaetocalyx, from the Coconino County portion of the Grand Canyon, including several from the Grand Canyon Village area. Interestingly, all of the vouchers except one are from the flats on the Rims. The exception is one voucher from Surprise Valley, just south of where Thunder River and Deer Creek Trails meet, which is probably another flattish area.

The plants here are on a steep southwest-facing, very hot hillside composed almost entirely of gravel and pebbles.

First occurrence on South Kaibab Trail: mile 1.25, elevation ~6100 feet (~1860 m).

Number of plants along Trail: at least 10 plants were found in at least 2 different locations in August 2008.

Pictures

From 23 August 2008, mile 1.25, 0.04 miles above Cedar Ridge:

The next picture shows the top side of the stems, with the separate stipules circled. Click on picture to get original picture.

The next picture shows the bottom side of the stems, with the fused stipules circled. Click on picture to get original picture.

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From 16 September 2006, from the same location:

In the next picture, note the pink gland appendages in about half the flowers.

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/chamaesyce_polycarpa.html
Comments and feedback: Tom Chester
Last Update: 6 September 2008