Plant Species of the South Kaibab Trail:
Adonis blazing star, Mentzelia multiflora

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

I treat Arizona plants determined as Mentzelia pumila as synonymous to M. multiflora. This follows the Christy Vascular Plants of Arizona 1998 treatment, the latest one for the Arizona plants, as well as SEINet.

Kearney and Peebles also treated all these plants as a single species under the name of Mentzelia pumila. They considered M. multiflora simply a variety of M. pumila, and said all the varieties intergrade so completely that it is scarcely worth while to maintain them, with no geographic separation.

The Vascular Plants of Arizona 1998 treatment calls all of these plants M. multiflora, saying the name Mentzelia pumila (Nuttall) Torrey & Gray was misapplied by Kearney and Peebles, and others.

However, be aware that not everyone follows this 1998 treatment, with two later treatments maintaining the separate existence of both M. pumila and M. multiflora in Arizona and Utah. In particular, USDA Plants still accepts the name M. pumila (Nuttall) Torrey & Gray for these plants, as does the 2003 Utah Flora. And just to add to the confusion, apparently another author published the same name, and that name, M. pumila Kuntze, is considered by the Utah Flora as synonymous with M. multiflora, even while maintaining M. pumila (Nuttall) Torrey & Gray as a separate species.

Unfortunately, there is considerable disagreement as to how to discriminate M. pumila and M. multiflora (see below), as well as exactly how many subspecies or varieties there are of these species. Until more work is done to show whether there are in fact multiple taxa here, it seems wisest to follow the 1998 treatment.

Diehard taxonomists can consult the end of this page for a discussion of the claimed differences between M. multiflora and M. pumila. Except in that discussion, I use the names to mean the same set of plants. For those who consider these species different, I will retain the names used by each source in quotes from each source, even while considering them to be synonymous.

Another common name for this species is stickleaf.


Identification status: High confidence to the species pair M. pumila / M. multiflora, which I will call M. multiflora in the plant guide and flora.

In southern California, Mentzelias are often difficult to key, since at least two species are discriminated only by their seeds. But the McDougall Grand Canyon key is a delight, since it uses only characteristics that are clear in the field. This key is especially delightful because it talks about fresh specimens, which are rarely discussed in a key. Keys are usually based entirely on pressed, dried specimens. (;-)

As mentioned above, I will retain the original names given in all sources quoted below.

The McDougall keying of these plants is:

3' Petals more than 1/4 inch long
4' Petals bright yellow when fresh

5  Stems erect, not branched from the base ...Mentzelia pumila
5' Stems much-branched from the base, often partly prostrate ... M. puberula

McDougall did not have a separate M. multiflora in his Grand Canyon Flora.

Only couplet 5 gives a bit of difficulty, which is easily resolved when one discovers that M. puberula is a perennial, with lots of weak stems at ground level, whereas M. pumila in the Grand Canyon is a biennial, with just a few stout stems coming from ground level.

The Kearney and Peebles key to discriminate these two species is clearer:

9  Stems usually tall (40 cm or longer) and erect, seldom branched from base,
herbaceous; leaves mostly linear or oblong, sinuate-dentate to pinnatifid,
rarely nearly entire; petals 10 to 20 mm long; capsules 10 to 20 mm long,
acutish to rounded at base ...Mentzelia pumila

9' Stems low (seldom more than 30 cm long), commonly decumbent, diffusely
branched from the base, often suffrutescent; leaves oblong, ovate, or somewhat
obovate, shallowly toothed to nearly entire; petals 8 to 10 mm long; capsules 9
to 12 mm long, rounded at base  ... M. puberula

Kearney and Peebles placed M. multiflora as variety multiflora under M. pumila.

This is another great key, with many good characteristics, and actual numeric definitions of what is meant by "tall" and "low". (;-) The plants on the South Kaibab Trail are tall, erect, and herbaceous, clearly fitting M. pumila. (I don't have any numeric measurements of the petals and capsules, and the other leaf and capsule characteristics of these plants are consistent with either species.)

The plants key to M. multiflora in the Christy treatment as well, which I won't reproduce here due to its length.

Those who don't like to use keys can simply compare my photographs below to the following two photographs to see the difference between these species: M. pumila = M. multiflora and M. puberula.

Huisanga, Makarick and Watters 2006 say that M. pumila is the most common ...[Mentzelia] species in the Grand Canyon. They also report the interesting fact that the flower of this species opens in the later afternoon and closes around sunset. This is my kind of flower, open in the later part of the day when I am hiking, instead of the one that opens only in the early part of the day when I am sleeping or traveling to a trailhead! (;-) This species is much more civilized than our showiest Mentzelia species in southern California, Mentzelia laevicaulis, which typically doesn't open its flowers until after sunset and then closes them by noon.

I was very surprised to read that the flower is only open for a handful of hours. Many flowers that open in the later afternoon stay open at night. But it appears to be true; Glad (1975) says that a related Mentzelia species receives most of its pollinating bumblebees from about two hours before sunset until it is nearly dark.

Quite by accident, I photographed the flowers opening as I returned to the South Kaibab Trailhead on 23 September 2008. The following pictures are not of the same flowers, but are from plants at progressively-higher elevation, except for the first one photographed on the way down. The photographs are labeled by time.

12:08 p.m.
3:28 p.m.
3:30 p.m.
4:33 p.m.

The flower structure for this species is very interesting, especially since there are different interpretations of the flower parts! The following picture has flower parts labeled (the unlabeled picture is at the bottom of this page):

In the above picture, the 5 sepals are the very un-petal-like salmon/orange-colored linear parts attached to the top of the ovary / fruit, hidden behind the other flower parts when the flower is fully open, and persistent in fruit.

In the interpretation of Christy, there are 5 petals and 5 staminodes that appear petal-like. This interpretation is consistent with the 5 petals in all the other Arizona Mentzelia species.

A staminode is a modified stamen which is sterile, bearing no pollen (Harris and Harris 2001). Some of the tips of these staminodes bear a significant resemblance to the outer stamens, and look like they are trying to have anthers, supporting this interpretation. However, the Utah Flora calls these staminodes petals, and simply says this species has 10 petals.

The outer stamens have wide filaments that resemble petals, labeled Petal-like stamens in the above picture.

If flowers are open, it is easy to identify this species in the field since this is the only Mentzelia species at the Grand Canyon with what appears to be 10 petals. Four species all have what appear to be 5 petals, and three species have a variable number of petals, from 5 to 10.

From a SEINet search on 6 September 2008, there are 11 vouchers of M. pumila / M. multiflora from the Coconino County portion of the Grand Canyon. The nearest are at: Grand Canyon Village; and above Phantom Ranch & Creek. Note that there may be additional vouchers at other herbaria not available through SEINet.

The 1987 Grand Canyon Flora gives an elevation range of 2000-4500 feet for M. pumila, and 1750-7000 feet for M. multiflora, with much overlap in their distribution.

First occurrence on South Kaibab Trail: mile 1.85, elevation ~5500 feet (~1675 m).

Number of plants along Trail: at least 40 plants were found in at least 9 different locations in August 2008.


From 24 August 2008, mile 1.85:

From 24 August 2008, from an unrecorded location at mile 1.85 or somewhat farther down the trail:

Discussion of M. multiflora versus M. pumila

Kearney and Peebles differentiate M. multiflora (as a variety of M. pumila) and M. pumila as follows:

2  Petals 15-20 mm long, obtuse (often appearing acute in dried specimens);
   outer filaments narrow ...var multiflora
2' Petals 10 to 15 mm long, acute or short-acuminate;
   outer filaments broad ....M. pumila (typical)

But Kearney and Peebles also say All the varieties intergrade so completely that it is scarcely worth while to maintain them.

The Utah Flora discriminates these species as follows:

15  Capsules typically 2 to 3 times longer than broad;
    petals sometimes ciliate apically; seeds narrowly winged ... M. pumila
15' Capsules main 1 to 2 times longer than broad;
    petals and seeds various ...(leads to) M. multiflora

The Utah Flora essentially negates the Kearney and Peebles discrimination of these two species. It says the petals of M. multiflora are 9-17(20) mm long and the petals of M. pumila are 9-15 mm long, and doesn't even mention a difference in the petal tips or outer filaments.

It is often a danger flag when floras disagree as to how to separate taxa that possibly are not distinct.


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Copyright © 2008 by Tom Chester.
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Last Update: 7 September 2008