Plant Species of the Borrego Desert: Cactaceae

Mammillaria dioica
California fish-hook cactus

Mammillaria tetrancistra
fish-hook cactus

Fig. 1. Left: Mammillaria dioica, California fish-hook cactus, photographed on 14 March 2008 in Henderson Canyon.
Right: Mammillaria tetrancistra, fish-hook cactus, photographed on 13 October 2010 in Cool Canyon, Earthquake / Shelter Valley, five days after a monsoonal rain event.
Click on the pictures to get larger versions.

Table of Contents

This page is a work in progress, so not everything in the Table of Contents is yet present.

Origin and Meaning of Name
Distinguishing Characteristics
Pictures of Young Plants, Mature Plants, and Dead Plants
Habitat, Distribution and Abundance
List of things to add to this page


We have a special fondness for our little Mammies in the Borrego Desert. Two of us (James Dillane and Vince Balch) are actually specialized mammy detectors, able to sniff out mammy habitat and spot them long before the rest of the authors and other mere mortals can do so. Where some of us find only a handful of mammies, those two can spot literally a hundred mammies.

Mammies like to hide at the base of boulders, rocks, barrel cactus, as well as in crevices on cliffs or tucked into rocks. Their coloration often blends into their environment, making them additionally hard to see, unless they are in flower. The flower of M. dioica is on the subtle side, but the flower of M. tetrancistra is strikingly apparent.

Flowers of M. dioica are often seen, since some plants begin to flower early in the January to March desert season, and a succession of buds on each plant, and later buds and flowers on other plants, allows the species to be in flower over a fairly long interval. Each plant produces a ring of flowers around their barrel, sometimes with just a few flowers open at a time, and others with a showy display of many flowers on multiple stems on a single plant.

But few people ever see the flower of M. tetrancistra, since the plants in an area bloom for only for a few days 5-6 days after the first monsoonal rain in August through October. Many websites and books only have pictures of the fruit of this species instead of flowers! Tom was alerted to a bloom one year by Kate Shapiro, but delayed going for a few days, at which point all the flowers were done, which really surprised him. Tom wasted no time in going the next year he was alerted by Kate that buds were present, going the next day.

Mammies are typically small, ~10-15 cm (4-6 inches) high, but can get as tall as 30 cm (one foot) tall. Baby mammies can be smaller than a thumbnail!

Distinguishing Characteristics

Our two mammy species are easy to tell apart when they have buds or flowers, but take a bit of care to distinguish at other times. Many is the time we've been unable to come to a consensus in the field about a particular plant, which was only resolved by looking at our photographs at home.

If there are buds or flowers, and it isn't five days after a monsoonal rain in the summer or early fall, it is M. dioica. If the flower is mostly white, perhaps with a pink stripe along the middle of each petal, it is M. dioica. If the flower is hot pink, perhaps with a bit of white, it is M. tetrancistra. See the pictures of the flowers at the top of this page.

Without flowers or buds, most of the time, one can fairly clearly get the determination in the field by eye, perhaps with a hand lens, by examining the spines. There is a single cluster of spines on each of the tubercles, which often form a dense latticework of spines, sometimes making it difficult to separate each cluster. The separate clusters can be seen fairly easily in the picture of M. dioica at the top of this page, but require a bit more examination to see them in the photograph of M. tetrancistra there.

Thus at times one has to take a good macro picture of the spines, and make the determination at home from the picture. This is especially the case when the plants are not swollen with water, and the stems have shrunk so much that it is hard to clearly separate the spines of one areole from its neighbors. In the field, one risks getting pricked by the center spines while trying to count the radial spines and keep one's place. Counting the spines on a photograph poses no such danger at home, although one has to be careful not to poke one's monitor.

Fig. 2 shows a side view of one spine cluster from a dead plant of M. dioica, and one from a dead plant of M. tetrancistra. See also a top view with a mm scale of these same spines.

Fig. 2. Spine clusters found detached from very dead plants (that were breaking apart) from M. dioica (left) and M. tetrancistra (right). The spine cluster of M. dioica was from an especially dead plant, and the spines have lost their normal white color.
Although there is a dramatic difference in size in the photographed spine clusters, this is not a reliable characteristic since they both typically have radial spines 6-10 mm long.
Click on the picture for a larger unlabeled version or see a top view with a mm scale.

Note that it will never be this easy to distinguish these characteristics in the field! Viewing a detached spine cluster is just the best way to see and learn the distinguishing characteristics. Please don't try to remove a spine cluster from a plant in the field unless it is dead!

A spine cluster is made out of two types of spines:

The three best characteristics (when there are no flowers) that separate these two species are:

Number of radial spines. M. dioica has noticeably fewer radial spines, just 11-22 per areole. Although M. tetrancistra is said to have 30-60 spines in the Jepson Manual, our plants only have 26-35 radial spines.

When the plants have imbibed a lot of moisture, swelling their diameter and separating the spine clusters, this is a piece of cake to use to determine the species, since the difference in number of radial spines is typically close to a factor of two. See Fig. 3.

Fig. 3. Left: Mammillaria dioica, California fish-hook cactus, with typically 14 radial spines per areole, photographed on 19 December 2005 on the California Riding and Hiking Trail above Hellhole Canyon.
Right: Mammillaria tetrancistra, fish-hook cactus, with 26-35 radial spines per areole, photographed in Mine Wash on 3 February 2011.
Click on the pictures to see the entire plants.

The increased number of radial spines often makes M. tetrancistra noticeably whiter from a distance. However, a very white appearance doesn't guarantee the determination, since a plant of M. dioica that has lost most of its stored moisture will also appear very white, since the spine clusters are much closer together.

Number of central hooked spines. To our knowledge, M. dioica always has just a single hooked central spine that sticks straight up, perpendicular to the plane of the radial spines ("erect"). M. tetrancistra typically has three hooked central spines in the Borrego Desert, but it is said to have as few as one and as many as four hooked central spines. James Dillane noticed that none of these three central spines are erect, being usually at an angle of about 30°. A review of a lot of our pictures shows no exceptions to that rule in that set of pictures. This is sometimes the easiest characteristic to see in the field.

The number of central hooked spines is often very difficult to see in a photograph since a closeup of the radial spines will usually not show the tips of the hooked central spines, and a more distant photograph will make it hard to see where the bases are of the central spines. It is visible in Fig. 2 only because the spine clusters are detached so that the central spines could all be in closer focus. However, a closeup picture will nearly always show whether there is one erect central spine or two to four spines at an angle of about 30°.

Number of "ranks" of radial spines. The reason that M. tetrancistra has about twice as many radial spines as M. dioica is that it has two or three layers of radial spines, called 2-3 ranks in the Jepson Manual. There wouldn't be room for it to have twice as many radial spines if it tried to fit them all into a single plane. Fig. 4 shows the difference in the plane of attachments for the radial spines.

Often the easiest way to observe this in the field or in a photograph is to look at the spine bases to see if any are "on top of" any other base. This would never be seen for M. dioica since its spines are well spaced radially and the bases of even close spines are "side by side", not "one on top of the other". In contrast, it is fairly easy to see some spine bases of M. tetrancistra being on top of other spine bases, especially in photographs taken showing spine clusters from near their side.

Mammillaria dioica
Mammillaria tetrancistra
Fig. 4. Photographs showing the difference in the number of ranks (= layers) for the attachment points of the radial spines. Left: Mammillaria dioica, with only a single ring of attachment points, all in the same plane. Right: Mammillaria tetrancistra, with three ranks of radial spines shown by the black lines, with the spines radiating out at their base at angles of something like 70°, 90°, and 110 °, as measured from the direction looking straight at the spine cluster on the plant. Note that the lower spines, radiating out at ~110°, curve so that most of the spine is parallel to the spine above it. If it didn't do that, the spine would end up inside the plant!
Click on the photographs for larger versions.

The presence of bristles in the axils between the tubercles also separates the species, but this is often hard to observe. M. dioica has bristles present in some axils, whereas M. tetrancistra never does. Hence if you observe bristles, you've confidently determined M. dioica. However, if you do not observe bristles, you do not know the determination for sure, since you may just have a specimen of M. dioica without axillary bristles in the portion of the stem you examined.

Fig. 5 shows a specimen of M. dioica with obvious axillary bristles and one with some axils without axillary bristles, and some axils with obscure bristles.

Fig. 5. Mammillaria dioica, California fish-hook cactus. Left: specimen with obvious axillary bristles between the tubercles, photographed in Glorietta Canyon on 22 February 2011. Right: specimen with some axils without bristles, and others with obscure bristles, photographed in Henderson Canyon on 29 December 2008.
Click on the pictures to see the entire plants.
For pictures with the axillary bristles circled, see Glorietta Canyon and Henderson Canyon.

Pictures of Young Plants, Mature Plants, and Dead Plants

Click on the photographs for larger versions.

Mammillaria dioica
Glorietta Canyon, 11 February 2013, showing three branches from lower stem Glorietta Canyon, 11 February 2013, showing seven branches from upper stem Crested form, side view (location deleted to protect the plant from collectors). See also The Rare Sonoran Hook-Snake. Crested form, top view (location deleted to protect the plant from collectors)

Pistillate flower, with sterile anthers (without pollen) and possibly-longer stigmas, Smuggler Canyon, 15 January 2014

Bisexual flower, with fertile anthers with abundant pollen and possibly-shorter stigmas, Glorietta Canyon, 22 February 2011.

Habitat, Distribution and Abundance

Fig. 6 shows species distribution maps that have been made from about 25% of our observations and from all voucher locations from the Consortium of California Herbaria obtained from a search on 9 February 2013. The maps in Fig. 4 are linked to larger maps maps that are at the same scale, and can be opened in two separate windows and blinked (align the two windows and use alt-tab on a PC to switch back and forth between the two maps).

Mammillaria dioica
Mammillaria tetrancistra
Fig. 6. Species distribution maps made from accurate GPS locations from about 25% of our observations and from all vouchers with georeferenced locations that are often only approximate. Left: Mammillaria dioica. Right: Mammillaria tetrancistra.
Click on the maps to see maps covering a larger area.

The vouchers have not been reviewed for accuracy, and hence a few of their positions and determinations may be incorrect. For example, this voucher from Jepson of Mammillaria tetrancistra is almost surely M. dioica, from this plant being in flower on 21 April and his description of the petals whitish with broad brown central band. We will review the vouchers in the future to produce a cleaner map.

M. tetrancistra is the only one found in the driest areas farthest out in the desert, such as the four vouchers from the south-facing slopes at the southeastern tip of the Santa Rosa Mountains near the Salton Sea. As one moves toward wetter habitats to the west, it is often found preferentially on dry hot sunny south-facing slopes, with M. dioica occupying most of the habitat. However, oddly, yet farther west, in even moister environments, in the San Felipe / Shelter / Earthquake Valleys, the two species seem to be intermixed with no clearly habitat separation.

Direct links to larger-scale species distribution maps, with information about the number of locations:

Note that there will usually be fewer locations shown on the map than the sum of all the locations from vouchers and our observations, since some voucher locations are not distinct, and some of our observations and voucher locations are of the same location.

List of things to add to this page

Delay between flower and fruit.

Sponginess of stem.

Odor of flowers.

bloom times.

# of stems.

Origin and Meaning of Name

Pictures of Young Plants, Mature Plants, and Dead Plants

Habitat and Abundance

Check why the color of the ribs looks so different in Fig. 3 between the species.

Give summary of differences between species when not in flower:

Voucher data provided by the participants of the Consortium of California Herbaria (

Geographic distribution maps made with BerkeleyMapper .

Go to:

Copyright © 2013-2014 by Tom Chester, Vince Balch, Mike Crouse, James Dillane, Kate Harper, RT Hawke and Kate Shapiro (authors listed alphabetically after the first author)
Commercial rights reserved. Permission is granted to reproduce any or all of this page for individual or non-profit institutional internal use as long as credit is given to us at this source:
Comments and feedback: Tom Chester
Updated 4 March 2014