Growth form and stem maturity
New stems arise mainly near the bases of existing axes. A single plant may bear many short green stems and a few taller axes with pseudocephalia. This flowering zone, covered by long spines, develops as a continuation of the same stem. In the studied Llanos de Magdalena population, its initiation occurred at an average stem height of about 93 cm, with the threshold varying with plant size. [Martorell et al. 2006]
Habitat and population regeneration
In southern Arizona, senita occupies habitats including depressions and the margins of ephemeral washes. Parker and Hamrick studied eight populations in Organ Pipe Cactus National Monument. Six sites were on flats or basin floors with coarse sandy soils and two on slopes. These settings expose plants both to water movement during heavy rain and to cold-air drainage on clear winter nights. [Parker and Hamrick 1992]
A leaning stem can root after contacting the ground while initially remaining attached to its parent. Detached fragments can also establish roots. Floodwater may move them downstream along an ephemeral wash. In northern populations, this mode of regeneration coexists with less frequent seedling recruitment whose success depends on favourable environmental conditions. [Parker and Hamrick 1992]
Clonality and genetic variation
Allozyme analysis identified 87 multilocus genotypes among 336 plants from eight Arizona populations. Repeated genotypes usually occurred close together, although some were also found farther apart. This pattern is consistent with local clonal expansion and occasional fragment transport. Vegetative reproduction coexisted with substantial diversity, also sustained by sexual recruitment and gene flow. [Parker and Hamrick 1992]
Green surface area and reproduction
Martorell and colleagues measured 317 plants in Baja California Sur and counted their flowers and fruits near the end of the season. The greatest current production of these structures was associated with an intermediate proportion of stem length covered by pseudocephalia. Very extensive coverage accompanied lower reproductive output. The authors relate this pattern to a balance between flower protection and light reaching green surfaces. The role of shading remains an interpretation of morphological data because photosynthesis was not measured directly. [Martorell et al. 2006]
Internal woody connections
In the decomposing skeleton of a tagged Arizona plant, Gorelick described woody projections extending from the vascular cylinder towards the areoles. He suggested that secondary lignification of vascular traces could stiffen the fleshy stems. This functional hypothesis rests mainly on documentation of one specimen. The contribution of these structures to load bearing requires direct mechanical testing. [Gorelick 2016]
Flowers and insect interactions
Senita flowers open in the evening and require compatible pollen from another plant. In the Sonora study, female Upiga virescens moths were the main pollinators, actively depositing pollen on the stigma. Some of their offspring later developed in fruits. Decomposing stems instead provide breeding sites for Drosophila pachea, a fly adapted to the tissues’ distinctive chemistry. These interactions involve different plant parts and stages of tissue development. [Fleming and Holland 1998] [Heed and Kircher 1965] [Kircher et al. 1967]
Related articles
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Kaktologia 2009b] [Neciu n.d.]
Synonyms and names in the literature
Pachycereus schottii · Cereus schottii · Pilocereus schottii [2-WWW]