Armatocereus matucanensis

Name and scope of the evidence

Plants of the World Online accepts Armatocereus matucanensis Backeb. Its synonyms include A. mataranus and A. mataranus subsp. ancashensis. The accepted range extends from southern Ecuador to Peru. The results below concern material from Áncash identified in the studies as ancashensis. [2-WWW] [Rojas et al. 2026, POWO record 19747-2, 12 October 2026, pp. 1–3, 10]

For the cytogenetic study, fruits were collected in Cosma, in the district of Cáceres del Perú. The seeds produced seedlings from which root tips and young green stems were sampled. The authors retained the subspecies name to identify the population's origin. Their chromosome comparisons cover this population and can provide a reference for further studies within the genus. [Rojas et al. 2026, pp. 3, 10]

Germination in light and darkness

Jara-Peña and colleagues compared germination in fourteen Peruvian cacti. Seeds identified as A. mataranus subsp. ancashensis came from Áncash. Before the main experiment, their seed coats were abraded with fine sandpaper. Each treatment comprised five plates of 25 seeds on 1% agar. Observations lasted 30 days at 18–25°C. [Jara-Peña et al. 2024, pp. 4–6]

Under a photoperiod of 12 hours of light and 12 hours of darkness, 53.6% of the seeds germinated. Under continuous darkness, beneath a double layer of aluminium foil, 64.0% germinated. A seed was counted as germinated when its radicle reached 2 mm. The relative light germination index was 0.46. The seeds therefore germinated under both exposures in this experiment and were classified as indifferent to light. [Jara-Peña et al. 2024, pp. 6–8, Table 2, Figure 3]

The mean germination time reported in the table was 20.80 ± 0.45 days. This describes a scarified seed batch under a specified temperature and medium. The main light-versus-dark comparison was performed after that treatment. Its result does not establish how every untreated seed batch will respond to sowing. [Jara-Peña et al. 2024, pp. 4–8, Tables 1–2]

Chromosomes and ribosomal genes

In 2026, Rojas and colleagues counted chromosomes in 23 metaphases from root meristems. Sixteen showed 2n = 22, consistent with diploidy at a basic number of x = 11. Five preparations had 21 chromosomes and two had 20. The authors discuss chromosome loss or overlap during preparation as a possible explanation for the lower counts. [Rojas et al. 2026, pp. 4–5, 8–9, Figure 2]

Fluorescence in situ hybridization, which labels selected DNA sequences on chromosomes, revealed two 5S rDNA loci on different chromosome pairs. One lay near the centromere on a long arm and the other within the short arm of another pair. The 45S rDNA locus occurred at the end of the short arm of a further pair. The diploid complement therefore showed four 5S signals and two 45S signals. [Rojas et al. 2026, pp. 5–6, Figures 2–3]

DNA replication in the young stem

Flow cytometry covered young green stem tissue from five plants. The mean DNA content of a 2C nucleus was 2.73 ± 0.07 pg. Classes of 4C, 8C, 16C, 32C and 64C were also detected. This series indicates endoreduplication, repeated DNA replication without successive cell divisions. Nuclei within the same tissue can consequently contain different amounts of DNA. [Rojas et al. 2026, pp. 4–6, Figure 4, Table 1]

The study established chromosome number and DNA organization in this population. The authors relate the possible significance of endoreduplication to succulent water relations, but did not measure its effect on water storage or photosynthesis here. Resolving this requires comparisons of tissues and their physiology. The cytogenetic dataset also leaves taxonomic boundaries to be assessed alongside other populations and characters. [Rojas et al. 2026, pp. 10–11]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kaktologia 2009b, file p. 6] [Neciu b.d., file p. 1]