Ariocarpus fissuratus (Engelmann) K. Schumann was described in 1856 as a Mammillaria. This was the genus to hold globular, tuberculate cacti at that time. It was first known from Texas and adjacent Coahuila. Widely distributed in collections for a long time, it is very popular for its outstanding rock-like appearance of the stem and its beautiful pink to magenta flowers. The triangular star-like arranged tubercles with a fissured, greyish surface blend tremendously well with the limestone gravel of its habitat and make detection in the field a question of careful close-up scanning of the ground, unless the “living rocks” show their spectacular flowers. Cultivation is not too difficult in a greenhouse, although A. fissuratus grows extremely slowly. The plants need deep pots to accommodate the napiform unit formed by the stem base and the rootstock (or they will often simply crack your pots), and a well-drained substrate. A place near the roof of the greenhouse helps drying the pot after watering. This can be done weekly during summertime, if the weather is sunny enough, with a little fertilizer added. Kept this way, plants will show a healthy, although slow growth, and will produce their showy flowers in September and October. Don't forget to check the plants at that time, if they are placed on the upper shelves of your greenhouse.

The characters of typical A. fissuratus are a flattened stem apex with triangular, spreading, densely packed tubercles, about as long as wide. The base of the tubercles is ascending and smooth, hidden between the adjacent tubercles, whereas the upper half of the tubercle is spreading horizontally and shows a central longitudinal areolar groove on the upper side, with abundant wool, and a lateral longitudinal furrow on each side of the tubercle, along the edge. The surface is coarsely papillated (rather than fissured), with the papillae tending to be arranged in transverse lines, which are interrupted by the areolar groove and the lateral furrows. Hence, there are two longitudinal papillated fields on each side of the areole. The species name “fissuratus” (= fissured) refers to this remarkable surface structure.

A. fissuratus and A. lloydii

The shape of stem and tubercles of A. fissuratus shows some variability, which correlates to its north-south distribution. Whereas the typical form of the Big Bend region of Texas and along the Rio Grande is well documented by many collections, there are rather few collections from northern and central Coahuila. Occurences around Parras in southern Coahuila are well known. They are morphologically distinct and easily identifiable, showing rounded tubercles, lacking edges and lateral longitudinal furrows, and showing quite coarse, often confluent papillae which form transversal ledges. Not surprisingly, they were described in 1911 as a separate species, Ariocarpus lloydii Rose. Their distribution, as presently known, ranges from southern Coahuila and adjacent Zacatecas to eastern Durango (Nazas, Peñon Blanco).

From the region of Cuatro Cienegas in south-central Coahuila and from Estacion Marte in southern Coahuila, we know forms somewhat intermediate between A. fissuratus and A. lloydii (cf. Stuppy & Taylor 1989), which possibly correspond to plants described as Roseocactus intermedius Backeberg & Kilian 1960, with “northern Mexico” given as origin. These intermediate forms make it difficult to classify A. lloydii as a separate species, although the northern forms from Texas and the southern ones from around Parras are well identifiable. The combination as Ariocarpus fissuratus var. lloydii (Rose) W. T. Marshall was published in 1941. Stuppy & Taylor 1989 maintain var. lloydii, mentioning the intermediate forms. In their recently published study, Anderson & Fitz Maurice 1997 come to the conclusion, that even the status of a variety is questionable, because of the incomplete geographical and morphological separation.

A. fissuratus ssp. hintonii

A new taxon related to A. fissuratus showed up in 1981. Wild collected specimens had been observed in cultivation south of Matehuala in San Luis Potosí, quite outside the range of A. fissuratus (Lausser & Scherer 1984). The plant became known as A. fissuratus var. minimus Hort. (nom. nud.). In 1984 the habitat was located by George S. Hinton and today two sites in northern San Luis Potosí are documented. Comparison with A. fissuratus sensu stricto was rather obvious, and in 1989 the taxon was described as Ariocarpus fissuratus var. hintonii W. Stuppy & N. P. Taylor. Differences exist in the smaller stem, tubercles longer than broad, with sharper edges and a more delicate papillate structure of the surface with unarranged papillae, leading to a better contrasting of the slightly narrower lateral furrows. No differences have been observed in the flowers, but the seeds are notably smaller. The geographical isolation is unquestionable, the closest A. fissuratus (var. lloydii) occur some 150 km further north-west, across high mountain ranges (distribution map in Stuppy & Taylor 1989). The later combination as Ariocarpus fissuratus ssp. hintonii (W. Stuppy & N. P. Taylor) Halda 1998 corresponds with newer criteria of classification.

A. fissuratus ssp. bravoanus

The accidental discovery of a new Ariocarpus by Hector Hernández in 1991 in the Municipio Guadalcazar, south of Entronque Huizache in San Luis Potosí, was quite a surprise. It was described as Ariocarpus bravoanus H. M. Hernández & E. F. Anderson 1992. Comparison with A. fissuratus ssp. hintonii, which is located some 85 km to the north, was quite obvious. At the same time, A. bravoanus was compared with A. agavoides (Castañeda) E. F. Anderson, growing to the east at about the same distance (distribution map in Anderson & Fitz Maurice 1997), stressing the position of the areole in the centre of the upper surface of the tubercle in both A. bravoanus and A. agavoides (Hernández & Anderson 1992). However, A. agavoides lacks the characteristic papillae of A. fissuratus.

The surface structure of the tubercles is quite variable in A. bravoanus. Complete formation of the papillated fields can only be observed in large adult specimens. Here, there are two narrow papillated strips along the edge of the tubercle, separated by a weak furrow, the inner strip often consisting of a single row of papillae. Younger specimens may show only the outer papillate strip, or separation of the two strips may be faint. Without doubt, the most striking character of A. bravoanus is the areole, which may be round or slightly elongated and is situated in the smooth, concave centre of the tubercle. The position of the tubercles is rather ascending in A. bravoanus, whereas in A. fissuratus ssp. hintonii, tubercles are rather spreading. No differences in the flower are reported between A. bravoanus and A. fissuratus ssp. hintonii, and the seed of both taxa is similarly slightly smaller than in A. fissuratus ssp. fissuratus.

Anderson & Fitz Maurice 1997 came to the conclusion that A. bravoanus and A. fissuratus ssp. hintonii should be considered as a single species, consisting of two subspecies, A. bravoanus ssp. bravoanus and A. bravoanus ssp. hintonii (W. Stuppy & N. P. Taylor) E. F. Anderson & W. A. Fitz Maurice. The smaller size of the seeds was given as an important argument for this classification. Indeed, it is sometimes difficult to identify old specimens of the two taxa at first sight. However, as stated above, A. bravoanus is quite variable and certain specimens may differ considerably from A. fissuratus ssp. hintonii. Nevertheless, the classification of Anderson & Fitz Maurice is easily understandable. The authors just do not follow the opinion of Stuppy & Taylor 1989, that A. fissuratus ssp. hintonii and A. fissuratus ssp. fissuratus belong to the same species. Sharing aspects of both classifications, the combination A. fissuratus ssp. bravoanus (H. M. Hernández & E. F. Anderson) J. Lüthy was recently published (Lüthy 1999). Quite a logical conclusion, if one follows previous authors, as an overview can easily show:

Variable Areoles

The seedlings and juvenile stages of these taxa cannot be distinguished from each other. They first show the very slender, much elongated, ascending tubercles arising from a globular hypocotyl with a diminutive areole on the tubercle tip, bearing a few rudimentary spines, characteristic for the genus Ariocarpus. The following stages have triangular tubercles, irregularly papillated on the whole upper surface, allowing identification as A. fissuratus sensu lato. The tubercles then gradually grow broader and shorter. Only with age, when the fertile areoles and the papillate fields are formed, the taxa can be identified and the differences are considerable, especially if one compares ssp. fissuratus (or even its var. lloydii) with ssp. bravoanus, ssp. hintonii being rather intermediate between the former two. It has to be considered in this context, that likewise within ssp. fissuratus (including var. lloydii), the shape of the tubercles and the papillate fields show such an amount of variation, that these differences cannot be weighed too strongly. The remaining differentiating characters are the length and position of the areole. The rather loose arrangement of the more elongated tubercles in ssp. bravoanus leads to the exposure of the tubercle surface below the areole, whereas in ssp. fissuratus and ssp. hintonii, the base of the tubercle is covered by the spreading, densely set, overlaying tubercles. Likewise in ssp. fissuratus and ssp. hintonii, the areole, although it is quite elongated, does not reach the axil, but is located in the centre of the tubercle surface. The areolar groove in ssp. fissuratus and ssp. hintonii is formed by the prominent inner papillate fields, which are almost lacking in ssp. bravoanus. The areolar groove in ssp. bravoanus is only indicated by the concave centre of the tubercle and the sometimes slightly elongated areole. These differences in the areole morphology are regarded as of minor importance by Anderson & Fitz Maurice (1997), leading them to classify ssp. hintonii as conspecific with ssp. bravoanus.

In conclusion, it can be stated that no strong qualitative differences exist between A. fissuratus ssp. fissuratus, ssp. hintonii and ssp. bravoanus. There are instead strong similarities, particularly in the papillated fields on the upper tubercle surface, that are not observed in other species of the genus.

Note. The description of Ariocarpus fissuratus var. hintonii caused quite a sensation, surpassed by the following description of Ariocarpus bravoanus. In spite of national Mexican as well as international legislation, both taxa are widely distributed in collections already, and accordingly heavily decimated in habitat. Whereas A. fissuratus ssp. hintonii is on sale now as juvenile, artificially propagated specimens, we still have to wait for artificially propagated A. fissuratus ssp. bravoanus.

References

Anderson, E. F. & W. A. Fitz Maurice 1997: Ariocarpus revisited. Haseltonia 5: 1-20.
Hernández, H. M. & E. F. Anderson 1992: A new species of Ariocarpus (Cactaceae). Bradleya 10: 1-4.
Lausser, A. & E. Scherer 1984: Eine interessante Zwergform von Ariocarpus fissuratus (Engelmann) K. Schumann. Kakt. and Sukk. 35 (8): 185-187.
Lüthy, J. 1999: Einige neue Kakteennamen. Kakt. and. Sukk. 50 (11): 277-280.
Stuppy, W. & N. P. Taylor 1989: A new variety of Ariocarpus fissuratus (Cactaceae). Bradleya 7: 84-88.

Illustrations:

• Fig. 01: (Cover Picture) A. fissuratus ssp. fissuratus in the Big Bend Region of Texas

• Fig. 02: A. fissuratus ssp. fissuratus flowering in early October near Cuatro Cienegas

• Fig. 03: A. fissuratus ssp. fissuratus from Texas in cultivation, flowering in a pale pink.

• Fig. 04: Tubercles of A. fissuratus ssp. fissuratus (ZSS 981490)

• Fig. 05: A rather typical A. fissuratus ssp. fissuratus near Cuatro Cienegas

• Fig. 06: A. fissuratus ssp. fissuratus from Texas

• Fig. 07: A. fissuratus var. lloydii growing near Parras in southern Coahuila

• Fig. 08: A. fissuratus var. lloydii tends to grow to globular or even columnar shape in cultivation

• Fig. 09: Tubercles of a typical specimen of A. fissuratus var. lloydii(ZSS 981491)

• Fig. 10: A. fissuratus var. lloydii (old cultivated specimen), showing rounded tubercles without lateral furrows

• Fig. 11: A. fissuratus ssp. hintonii (confiscated specimen) with pointed, keeled below and sharp-edged tubercles

• Fig. 12: A. fissuratus ssp. hintonii (ZSS 981498)

• Fig. 13: A. fissuratus ssp. hintonii: a small specimen, difficult to detect

• Fig. 14: A. fissuratus ssp. bravoanus (confiscated specimen)

• Fig. 15: A. fissuratus ssp. bravoanus at the type locality

• Fig. 16: Variation of the papillation in A. fissuratus ssp. bravoanus

• Fig. 17: A. fissuratus ssp. hintonii The extent of the areole towards the tubercle axil