Five samples and current names
In 2012, Řepka and Gebauer compared spines of five taxonomic units then assigned to Escobaria. These were the current Pelecyphora abdita (called Escobaria abdita in the paper), P. hesteri (E. hesteri), P. minima (E. minima) and two samples of P. missouriensis. The material had documented provenance. P. abdita plants came from El Oro in Coahuila, P. hesteri and P. minima from near Marathon in Texas, and the two other samples from Electric in Montana and Holbrook in Arizona. [Řepka and Gebauer 2012, pp. 138, 140, Table 1]
Plants of the World Online includes the former E. missouriensis subsp. navajoensis in P. missouriensis subsp. missouriensis. In the study, the Arizona and Montana material had different characters and separate results. When comparing them, we retain the identifications used by the authors. The current shared subspecies name therefore encompasses two historically distinguished samples, with their individual results retained. [2-WWW]
How the spines were prepared
Material was collected from three areoles of plants maintained in cultivation. An areole is a specialised stem region from which spines grow. Whole areoles were photographed under a stereomicroscope, then hydrated for 24 hours in a mixture of water and glycerol. Three spines were taken from each for sections and three for surface examination. Sections were prepared by hand and stained with phloroglucinol and hydrochloric acid to reveal lignin in cell walls. Observations were made with a light microscope. [Řepka and Gebauer 2012, p. 141]
15 measurements were made for each cell character. The largest and smallest cell diameters in section and wall thickness were determined, and results were recorded as means with standard errors. The number of measurements describes a series of cellular dimensions. The article does not state the number of individuals per taxon. The values obtained characterise the prepared material from identified cultivated plants. [Řepka and Gebauer 2012, p. 141, Table 2]
Hairs arising from the spine surface
The epidermis, the outer cell layer of the spine, was sclerified. This means that its cells had strongly thickened walls and their interiors remained empty in mature tissue. In four of the units studied, surface cells were approximately rectangular in section. In P. abdita, they had more oval outlines. The surface of its short, finger-like spines could appear porous, but examination revealed an arrangement of closed cells. [Řepka and Gebauer 2012, pp. 139, 143, Fig. 1]
Both P. missouriensis samples had trichomes on their spines, hairs formed as outgrowths of epidermal cells. They were unicellular and unbranched. Hairs were shorter on the Montana material and longer, often curved and more pointed, on the Holbrook sample. Surface images were matched by sections showing these outgrowths around the spine edge. The surfaces of the P. abdita, P. hesteri and P. minima spines studied lacked such hairs. The difference therefore concerns the structure of the spine itself and helps distinguish the samples compared. [Řepka and Gebauer 2012, pp. 139, 143–145, Fig. 1–2]
Four zones in Pelecyphora abdita
Sclerenchyma fibres, strengthening cells with secondarily thickened walls, were identified inside the spine. In the P. missouriensis, P. hesteri and P. minima samples, the epidermis surrounded a mass of these fibres. In transverse section, their outlines were rounded or elliptical, depending on the taxon. Thick walls left small cell lumina. The two-zone organisation therefore comprised a covering and a fibrous interior. [Řepka and Gebauer 2012, pp. 143–145, Fig. 2]
In P. abdita, an additional subsurface zone lay between the epidermis and fibres. Beneath it were larger fibres in the outer portion, while smaller fibres with thicker walls formed the centre. The authors distinguished four zones, although the subsurface zone could contain one or two cell rows. The term “four-layered spine” describes this recurring tissue arrangement. Fibre dimorphism, with larger cells outside and smaller cells in the core, was a distinctive character of this sample. [Řepka and Gebauer 2012, pp. 141, 143–145, Table 2, Fig. 2A]
Cell size and wall thickness
The large epidermal cells of P. abdita had a mean maximum diameter of 48,4 µm. In the other samples, it was 13,3–22,8 µm. This difference becomes visible only in section. The length of the whole spine, the size of its constituent cells and their wall thickness describe separate structural levels. In P. abdita, short spines combined large covering cells with smaller cells in the core. [Řepka and Gebauer 2012, pp. 141–142, Tables 2–3]
| Material studied | Epidermis | Core fibres |
|---|---|---|
| P. abdita (E. abdita) | 3,0 | 2,4 |
| P. missouriensis, Montana sample (E. missouriensis subsp. missouriensis) | 4,5 | 3,7 |
| P. missouriensis, Arizona sample (E. missouriensis subsp. navajoensis) | 3,6 | 4,0 |
| P. minima (E. minima) | 3,6 | 3,3 |
| P. hesteri (E. hesteri) | 4,2 | 3,8 |
The core fibres of P. hesteri had walls with a mean thickness of 3,8 µm. The authors described the structure studied as lignified, referring to an earlier description of these spines as corky. An external impression of lightness or a similar colour may accompany different cell arrangements. Assessment in section allows this difference to be assigned to a specific tissue. [Řepka and Gebauer 2012, pp. 141, 144, Table 2]
Anatomy in species identification
The distinctness of P. abdita was assessed by combining spine characters with the structure of the whole plant. In the 2012 comparison, it was distinguished by a short, often comb-like spine arrangement, a single stem, a napiform storage root and a rapidly drying mature fruit wall. The four-zone anatomy strengthened this set of diagnostic characters. Differences between species therefore came from several plant parts examined at different scales. [Řepka and Gebauer 2012, pp. 142–144, Table 3]
The consistency of spine characters within populations remains a separate question. The study provided detailed comparisons of five samples of known provenance. The authors identified the need to determine how much surface structure and anatomy vary between individuals and populations. They also considered whether the longer hairs of the Arizona sample might increase stem shading. This is a functional hypothesis. Testing it would require light and temperature measurements that account for spine-cover structure. The 2012 paper documented structures on which such a comparison can be based. [Řepka and Gebauer 2012, p. 144]
Micromorphological and anatomical spine features of selected Escobaria species (Cactaceae)
Řepka R., Gebauer R., Micromorphological and anatomical spine features of selected Escobaria species (Cactaceae), Bradleya, 2012, 30:138-146, doi: 10.25223/brad.n30.2012.a16
A comparison of spine surfaces and anatomy in five historically distinguished Escobaria taxa. Material comes from three areoles of cultivated plants of known origin. The authors describe epidermal hairs, cross-sectional structure and cell dimensions, and compare them with stem, flower and seed morphology. Four tissue zones in Escobaria abdita spines and hairs in two Escobaria missouriensis samples are the main differentiating traits.
Plants of the World Online — Royal Botanic Gardens, Kew
Accepted names, synonyms and distribution. A citation beside a taxon leads to its record.
Accessed 2026-10-08.
