Obregonia denegrii

Name and origin

Obregonia denegrii Frič is the name accepted in POWO, published in 1925. The database gives native occurrence in northeastern Mexico, in Nuevo León and Tamaulipas. Earlier combinations Ariocarpus denegrii and Strombocactus denegrii concern the same taxon. The species is associated with the desert and dry scrub biome. [2-WWW]

Ecological material primarily describes the Jaumave Valley in Tamaulipas. The IUCN profile from 1978 presents dry, stony limestone hills at about 800 m above sea level, with shrubs, rosette plants and other cacti. This is a description of specific habitats. The broader range now accepted in POWO also includes Nuevo León. [Lucas and Synge 1978, IUCN p. 107, Martínez-Berdeja and Valverde p. 1768] [Martínez-Berdeja and Valverde 2008, IUCN p. 107, Martínez-Berdeja and Valverde p. 1768] [2-WWW]

Tubercle rosette and flower

The stem is usually solitary, globular to slightly flattened, grey-green or dark green with a brown tint. The broad tubercles have an approximately triangular outline. On young tubercles, the areole is sheltered by white wool and bears a few thin, flexible spines. Overlapping tubercles form a dense rosette. [21-WWW]

According to the description cited in the study by Cardarelli et al., the body reaches about 12 cm in diameter. The older IUCN botanical profile gives 8–12 cm and tubercles 1–1,5 cm tall. Their tips produce 2–4 thin, slightly curved spines, about 1–1,5 cm long. They turn brown and fall off over time, so much of an older rosette may lack visible armature. [Cardarelli et al. 2010, p. 29 and p. 108] [Lucas and Synge 1978, p. 29 and p. 108]

A pale perianth surrounds yellow anthers and red-purple stamen filaments. Flowers appear in the woolly apical region. The fruit is elongated, initially fleshy and drying during ripening. It contains black seeds. [21-WWW]

Spindle-shaped roots form a distinctly thickened water store. This structure accompanies young plants’ capacity to change biomass allocation between root and shoot depending on substrate moisture. [Martínez-Berdeja and Valverde 2008]

The ecological study describes white flowers appearing in spring and summer. The older IUCN account associates their development with young areoles near the apex. The fleshy tubercles remain parts of the stem, and areoles are the sites where spines and reproductive organs arise. This arrangement helps identify the zone of new growth in the dense rosette. [Martínez-Berdeja and Valverde 2008, p. 1768 and p. 108] [Lucas and Synge 1978, p. 1768 and p. 108]

Water and seedling growth

In the greenhouse experiment from 2005–2006, six-month-old seedlings were observed for a further six months. For O. denegrii, two hydration levels were used, 25% and 60% of the water retained by the substrate after excess had drained, together with two light levels. Each treatment included at least seven seedlings. With greater water availability, relative biomass growth rate was higher and the root-to-shoot biomass ratio lower. [Martínez-Berdeja and Valverde 2008]

At two light levels, measured between 11 and 15 on a warm May day as about 102 and 243 µmol photons m⁻² s⁻¹, no significant light effect on the growth parameters analysed was found. These were greenhouse conditions, with weaker light than in a desert habitat. The result defines the seedlings’ response in this experiment, and the hydration values refer to the substrate used. [Martínez-Berdeja and Valverde 2008]

At hydration of 25% of the reference water amount in the substrate, the mean root-to-shoot dry mass ratio was 1,106 ± 0,353, falling to 0,774 ± 0,388 at 60%. The relative growth rate of the whole plant increased correspondingly from 0,007 ± 0,002 to 0,009 ± 0,003 g g⁻¹ day⁻¹. These are means ± standard deviation, pooled across the two light levels. The larger underground biomass share with less water available indicates a plastic growth response in the seedlings. [Martínez-Berdeja and Valverde 2008, Table 4, p. 1770]

Uprawa doniczkowa

Guidance from the Société Nationale d’Horticulture de France specifies a partly shaded position and a light, freely draining substrate with coarser mineral components. During growth, water after the substrate surface has dried. For cool overwintering below 10°C, the organisation recommends leaving the plant unwatered. Propagation is from seed. These are cultivation guidelines, separate from the seedling experiment described above. [21-WWW]

The pathway from seed to seedling in culture was studied in 2010. On moist, sterile filter paper at 25 ± 1°C, with 16 hours of light at about 40 µmol photons m⁻² s⁻¹, germination reached 72,7 ± 1,4% after 28 days. The sample included five replicates of 25 seeds each. The reported dispersion is the standard deviation. Another treatment, with seeds soaked in water and transferred to solid MS medium, gave 22,3 ± 1,0%. Germination therefore depended on the entire experimental procedure. [Cardarelli et al. 2010, p. 30 and table 1, p. 32]

In that second experiment, prior exposure of seeds to gibberellic acid GA₃ raised germination to 85,2 ± 0,9% after only seven days, with three replicates of 25 seeds each. The publication reports the GA₃ concentration differently in the methods and table, so it does not provide an unambiguous dose for reproducing the procedure. The result documents the response of the material studied to hormonal treatment. [Cardarelli et al. 2010, p. 30 and table 1, p. 32]

Areole activation and somatic embryos

Cardarelli et al. used four-month-old seedlings. On a common MS medium with growth regulators, longitudinally divided apices formed an average of 3,3 shoots per explant after 45 days, while individual tubercles formed about one. Whole apical fragments, basal portions and root portions produced no shoot proliferation at this stage. The result links propagation capacity with areole presence and the way the stem is cut. [Cardarelli et al. 2010, pp. 30–33]

In the next series, adding the synthetic cytokinin CPPU to the common medium increased shoot number to 5,0 ± 0,4 per explant. The medium also contained BAP and NAA, so CPPU was assessed as an additional component of this system. Shoots could arise directly from activated areoles. Callus present on cut surfaces was removed during subculturing to limit indirect regeneration through this tissue. [Cardarelli et al. 2010, p. 33–34, tabela 3]

Malda et al. had previously described both lateral and adventitious shoots and somatic embryos, embryos arising from vegetative cells. In the table for MS medium with BA and NAA, they reported 11,4 ± 6,2 shoots and 9,2 ± 5,3 embryos per explant over four months. The dispersion denotes the standard error of the mean. Regeneration capacity opens several propagation pathways, each involving further rooting and acclimatisation. [Malda et al. 1999b, tabela 1, p. 75]

Culture physiology and transfer to pots

In the study from 1999, cultures were maintained at 25–27°C, with a 16-hour light period and a photon flux of about 120–130 µmol m⁻² s⁻¹. Tissues of O. denegrii showed daily changes in titratable acidity, increasing in darkness and declining in light. Somatic embryos and in vitro shoots differed in acidity profile from one-year-old seedlings grown outside culture. The measurement used tissue extracts and indicated organic acid metabolism in CAM. [Malda et al. 1999b, metody p. 73–75, rycina 3a p. 79]

After transfer from culture, ambient humidity was gradually lowered and plants were placed in a 1:1:1 mixture of peat, perlite and coarse sand. Four months after acclimatisation, O. denegrii survival was 98% for plants spontaneously rooted in vitro, 75% for those rooted outside culture, and 93% for six-month-old plants obtained through somatic embryogenesis. The article does not give unambiguous group sizes for these percentages. The result concerns re-established growth in cultivation. [Malda et al. 1999b, p. 74 and table 3, p. 78]

Threats and propagation for conservation

Pressure from digging up plants for collections was already described in the IUCN profile from 1978. The micropropagation study from 2010 also notes the reduction of natural habitats. Slow growth and a small range make the fate of adult specimens and recruitment through seedlings separate conservation issues. [Lucas and Synge 1978, p. 107 and p. 29] [Cardarelli et al. 2010, p. 107 and p. 29]

In the official IUCN compilation from 2013, the species is listed as EN, Endangered. The change from the earlier VU category was marked with code N, referring to updated knowledge, data or application of criteria. This is the recorded assessment from 2013. Biotechnological plant production can support collections and conservation programmes, while representing genetic diversity requires material from a larger number of parent plants. Repeated propagation of one clone duplicates the same genotype. [26-WWW] [Malda et al. 1999b, IUCN pp. 1 and 7, Malda et al. p. 83]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kaktologia 2009a, file p. 7] [Kaktologia 2009b, file p. 15] [Neciu b.d., file p. 1]