Acanthocalycium leucanthum

Stem, flower and fruit

The Matagusanos population study describes a short columnar cactus reaching less than 100 cm in height and less than 25 cm in diameter. Its white flowers are funnel-shaped. The regional account places flowering between September and March, during Southern Hemisphere spring and summer. Ripe fruits split open to expose sweet pulp and numerous black seeds with a rough surface. [Almirón and Martínez Carretero 2010]

Monte vegetation and shrub shelter

Almirón and Martínez Carretero worked at Matagusanos in San Juan Province, in the Argentine Monte. They compared an alluvial plain with east-facing and west-facing slopes. Eight 6 × 10 m plots were established in each environment, and cactus positions were mapped relative to shrub canopies. Photosynthetically active radiation and temperature 7 cm above the soil were measured. Measurements covered the centre, intermediate portion and edge of shrub shade, together with open ground. They were taken at midday on days representing the four seasons. Combining plant maps with these environmental measurements allowed available cactus establishment sites to be compared. [Almirón and Martínez Carretero 2010]

Cacti were spatially associated with Larrea cuneifolia or Zuccagnia punctata, depending on the geotope. The relationship appeared at distances below approximately 1.6 m. Plant positions corresponded to changes in light availability between canopy centres and edges. This supports a role for local light heterogeneity in population establishment. The association itself is a field pattern, while direct effects on seedling survival require monitoring individual seedlings. [Almirón and Martínez Carretero 2010]

The authors related cactus positions to radiation beneath shrubs. In their analysis, variation in temperature near the soil did not account for these patterns in the same way. Plants thus occupied particular parts of the light mosaic according to slope exposure and shrub structure. This result concerns the observed distribution, allowing for different shrub effects under other habitat conditions. [Almirón and Martínez Carretero 2010]

Nocturnal flowers and diurnal pollinators

Gorostiague and Ortega-Baes found that flowers opened at night and remained available the following morning. The studied population was self-incompatible, so successful fertilization required compatible pollen from another plant. Visitors included moths, bees and passerine birds. Experiments controlling access by visitor groups showed a greater contribution of daytime animals to fruit and seed production than of nocturnal visitors. The extended floral lifespan consequently creates opportunities for contact with different pollen vectors. [Gorostiague and Ortega-Baes 2017]

Name and evolutionary position

POWO accepts Acanthocalycium leucanthum and retains Echinopsis leucantha as its synonym. Its 2012 transfer followed a chloroplast DNA analysis that placed the plant within the Acanthocalycium lineage. The sampled material included plants from Córdoba, San Luis and Catamarca. Nocturnal white flowers within this lineage illustrate evolutionary variation in pollination-related traits among closely related plants. [2-WWW] [Schlumpberger and Renner 2012]

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