Maihuenia patagonica

Habit and leafy short shoots

In Mauseth's material, cushions reached up to 2 m in diameter and about 35 cm in height. Open spaces remained between branches. Older axes, up to about 4 cm in diameter in the sample studied, often had dead and decaying sections, while living parts continued to produce leaves. These are dimensions of the specimens described, not limits to the species' size. [Mauseth 1999, p. 308]

Areoles may develop into short shoots that produce leaves near the same base over successive years. This creates clusters of leaves of different ages along the longer axes. Leuenberger documented fresh growth, maturing spines and older, yellowing leaves at the same time. This arrangement distinguishes the plant from the compact branching of M. poeppigii. [Mauseth 1999, Leuenberger, p. 80, ryc. 87–90] [Leuenberger 2008, Leuenberger, p. 80, ryc. 87–90]

Cushions in the Patagonian environment

The species occurs in Argentina and Chile. Plants on black volcanic deposits were described in Argentina's Payunia. The population used for the germination experiment grew in the Auca Mahuida reserve, in the transition zone between Monte and Patagonia. Seeds were collected from ripe fruit of 20 plants. [2-WWW] [Masini et al. 2014] [Leuenberger 2008]

Branches lying on the ground or partly buried may root. Dead cushion centres and living margins forming expanding clonal rings were observed in the field. New roots maintain contact between active plant parts and the substrate as the old centre gradually disappears. [Mauseth 1999, p. 308]

Inside an older stem

Young wood contains vessels, parenchyma and tracheids with broad thickenings. Older axes also develop large fibre clusters and intraxylary bark separating portions of wood. Mauseth described dead inner sections and living tissues farther out. He interpreted this arrangement as part of tolerating progressive death of portions of the axes under severe water stress. [Mauseth 1999, p. 310–314]

A diploid cytotype with 2n = 22 and a tetraploid cytotype with 2n = 44 have been described. Studies locating ribosomal genes showed a doubling of the number of particular signals in the tetraploid. The authors considered this evidence consistent with an origin through autopolyploidy, meaning multiplication of its own chromosome set. [Las Peñas et al. 2014]

Seeds and propagation

In the Auca Mahuida sample, seeds averaged 3.90 ± 0.30 mm long, 3.12 ± 0.25 mm wide and 1.86 ± 0.19 mm thick. A total of 100 seeds were measured, and the reported dispersion is the standard deviation. Seed numbers in 43 fruits ranged from 7 to 141. [Masini et al. 2014, tabela I]

Seeds were stored for 60 days at 5°C. The experiment then compared a control, 40 days of moist cold stratification, abrasion with sand and sandpaper, and removal of part of the covering with a scalpel. Each treatment included 10 replicates of 30 seeds. Germination took place under a 20/10°C cycle with 12 hours of light/12 hours of darkness. [Masini et al. 2014, pp. 192–193]

Only the scalpel treatment significantly increased the final proportion of germinated seeds relative to the control. The overall range of mean results across treatments was about 8–27%. The authors considered non-deep physiological dormancy, effects of the coverings and an excessively low experimental temperature. For sowing, this means distinguishing dead seeds from living seeds that remain dormant. The experimental procedures are compared in the article on germination of southern cacti. [Masini et al. 2014]