Flowers, fruits and young plants. Reproduction of Eulychnia

The flower's position on the northern side of the stem

On branched plants of Eulychnia breviflora, flowers arise laterally on columnar stems. Warren and colleagues recorded the directions of 180 buds and open flowers on 40 plants along about 100 km of Chilean coast. The northern side predominated relative to the stem axis and the centre of the whole plant. A subsequent study of Eulychnia acida assessed 300 reproductive structures on 20 plants from two sites. A strong northern pattern occurred here as well [Warren et al. 2016] [Warren et al. 2017].

At the Southern Hemisphere latitudes studied, the northern side faces the equator and receives abundant light. The authors suggest that proximity of the flower to strongly illuminated stem parenchyma may reduce the cost of supplying assimilates. Assimilates are products of photosynthesis that supply developing organs. A separate proposed effect is flower warming, which may influence insect behaviour in the cooler coastal environment [Warren et al. 2016] [Warren et al. 2017].

Direction measurements confirm the system's geometry. Sugar transport rate, flower temperature and the effectiveness of pollinator visits need to be assessed in separate experiments. Both orientation papers presented these mechanisms as testable explanations. The predominance of the northern side concerns the populations of two species studied and does not mean that every flower on every plant has a fixed position [Warren et al. 2016] [Warren et al. 2017].

From an enlarging bud to the fruit

A fuller cycle of E. acida was described through weekly observations of three Coquimbo populations from January 2006 to February 2007. Four external stems facing different directions were marked on each plant. The scale comprised eight stages. It began with a woolly areole and an enlarging bud. Perianth segments then appeared, the flower opened with visible stamens and pistil, and fruit developed after flowering [Salvatierra 2020].

Buds were observed from the end of the Chilean autumn, the main flowering period extended from spring to summer, and fruits ripened in summer. Successive stages occurred simultaneously on one plant. Individual plants also began and ended flowering at different times. The long period of flower presence across the population can therefore arise from overlap between shorter stages in many plants. Differences between sites included phase duration and the number of organs per stem [Salvatierra 2020].

In the seasonal data, a greater number of fruits per stem accompanied warmer conditions, while the association with relative humidity was negative. These were correlations observed as the season progressed. Temperature, humidity and organ maturity changed together, so the correlation coefficient alone does not establish the effect of one factor. The study did not establish the causes of bud and immature fruit loss [Salvatierra 2020].

Water can change seed number with similar flowering

In 2021, Piñones-Tapia and colleagues compared three E. breviflora populations at Caldera, Huasco and Coquimbo along an Atacama aridity gradient. At drier sites, flowers were smaller and plants displayed more of them. The bud phase was shorter, and flowering later and longer. Pollinator richness and visitation frequency were similar among populations. The site comparison thus connected variation in phenology and floral structure with environmental conditions [Piñones-Tapia et al. 2025].

Separately, thirty pairs of adult plants of similar size and architecture were matched at Coquimbo. One plant in each pair received 20 litres weekly from June to August, applied at its base over approximately 2 m². The other remained under natural drought conditions. Watering increased the number of seeds per fruit. Fruits per plant, measured floral traits and visitation parameters did not differ significantly between treatments. In this analysis, fruit production is the number of fruits per plant, as specified in the method and the figure presenting the result [Piñones-Tapia et al. 2025].

The positive seed response indicates that, in the dry year studied, plants could use additional water during seed production while retaining similar fruit numbers and observed visitation patterns. Differences among populations also encompassed conditions beyond water supply alone. The authors considered earlier bud preparation and population differentiation as possible reasons for the different response of floral traits. The manipulation describes a short-term response of adult cacti at Coquimbo [Piñones-Tapia et al. 2025].

A large fruit and different feeding methods

The fruit of E. acida has acidic pulp and remains closed until damaged or broken down. Ripe fruits can fall to the ground. In Las Chinchillas Reserve, fresh fruits were placed beside surfaces recording animal tracks. Tracks of the tinamou Nothoprocta perdicaria, the mockingbird Mimus thenca and the degu Octodon degus were found. In this trial, birds pecked the fruit without demonstrated seed swallowing. Degus carried whole fruits to burrows [Cares et al. 2018].

An experiment with degus allowed the fate of seeds after consumption to be studied. Most were destroyed during feeding and passage through the digestive tract. Under these conditions, the rodent acted primarily as a seed consumer. Simply moving a fruit from where it fell does not establish dispersal effectiveness. A new plant can arise only from a seed that survives transport and reaches a suitable germination site [Cares et al. 2018].

Seeds after passage through the digestive tract

In a separate comparison, fruits were fed to three goats and eleven guanacos. Feeding conditions were not identical. Goats received fruit as their sole food during experimental feeding, while guanacos also received other dietary components. Seeds were recovered from faeces, and only intact surviving specimens were selected for sowing. Seeds taken directly from ripe fruits formed the control group [Cares et al. 2018].

In each group, 100 seeds were sown individually in containers of gravel moistened with filtered water. Temperature was maintained at about 26°C, with a photoperiod of 14 hours of light and 10 hours of darkness. Radicle emergence was considered germination. During observations lasting up to 30 days, seeds recovered after goats reached 60% germination, controls 52%, and those recovered after guanacos 13%. The advantage of seeds recovered after goats over the control was not statistically confirmed [Cares et al. 2018].

The comparison concerns germination of seeds that could be recovered intact. The total proportion of seeds transferred into the field also depends on the amount of fruit consumed, seed destruction and the location where faeces are deposited. Different diets and small animal numbers further define the scope of the experiment. The result shows retention of germination capacity after passage through goats under the conditions studied [Cares et al. 2018].

Hypothesis of historical seed dispersers

The authors consider ecological anachronism, the persistence of fruit traits shaped in relationships with consumers that are now absent. The large fruits of E. acida may have been consumed by large herbivorous mammals. However, the historical role of extinct megafauna remains an explanatory hypothesis. The study of contemporary animals indicates which seeds survived the routes tested today and does not directly reconstruct past feeding on this species [Cares et al. 2018].

Outside the reserve, where goats occurred, a greater proportion of small cacti was found than in the compared patches inside. This result is consistent with a possible contribution of goats to seed transport. Existing vegetation patches with similar exposure were compared without random exclusion of animals. The balance also includes browsing, plant damage and substrate alteration. The effect on a particular population depends on the proportions of these influences [Cares et al. 2018].

A seedling needs the right microenvironment

Cares and colleagues followed young E. acida and Echinopsis chiloensis less than 30 cm tall at Las Chinchillas in 2009–2012. Their distribution was compared with the availability of individual shrub species and open space. E. acida occurred beneath Eriophyllum ambrosiodes, called Bahia ambrosioides in the paper, more often than expected from that shrub’s share of the habitat. E. chiloensis showed a corresponding association with Flourensia thurifera. Accounting for microhabitat availability distinguishes a species-specific association from the mere abundance of cacti beneath a common shrub [Cares et al. 2013][2-WWW].

Conditions beneath shrubs were cooler and had higher relative air humidity than open space. Growth of the young cacti already present was compared in open space, beneath F. thurifera and beneath the other shrubs. Mortality was assessed beneath shrubs pooled together and outside their cover. Differences between groups were nonsignificant in both analyses. Plant distribution therefore identifies conditions associated with earlier establishment, while subsequent monitoring describes survival of that existing cohort. The authors interpreted the specific shrub associations as possible nurse effects, also considering seed accumulation and microtopography [Cares et al. 2013].

More seeds from watered adult E. breviflora increase the potential supply of offspring, while conditions after dispersal determine their subsequent course. The E. acida study places that next stage within a particular arrangement of shrubs and open soil. Together, the papers show how water can affect reproduction during seed production and after seeds reach an establishment site. Each phase has its own outcome measure [Piñones-Tapia et al. 2025][Cares et al. 2013].

Observations of Eulychnia ritteri from Vizcachani in Peru provide a complement. In three patches studied in October 2018, only six seedlings were counted alongside 94 adult plants. Insects were observed on flowers, and fruits were eaten by Lagidium peruanum. The paper describes visits and feeding without a single-pollination trial or a test of seed germination after passage through the rodent. A one-time census indicates the structure of selected patches. Population recruitment is assessed by combining seed fate with survival of young plants over successive seasons [Pauca-Tanco et al. 2021].