Tacinga palmadora

Name and identification limits

Tacinga palmadora (formerly Opuntia palmadora) is a distinct, diploid species. Some material from Ceará previously described under this name belongs to T. mirim, distinguished in 2024. Identifying plants from the northwestern part of the historically reported range therefore requires attention to habit, flower structure and pericarpel characters. [Menezes and Alves 2024] [2-WWW]

Plant structure

It is a shrub with upright, flattened segments. The taxonomic comparison with T. lilae described plants 2–4 m tall, with segments 8–17 cm long and 3–7 cm wide. In the populations studied ecologically at Catimbau, plants averaged about 1,5 m. This comparison shows the importance of variation among populations and measurement conditions. [Majure et al. 2013] [Centeno-Alvarado et al. 2022]

Areoles are spaced 1–2 cm apart and can produce 2–9 spines, 0,2–3,5 cm long. In the ecological description studied, the orange or red-orange flowers are about 3–4 cm long. Fruits are obovoid to obconical, with whitish, yellowish or translucent pulp. The combination of fruit and pulp colour helps distinguish them from the white fruits of T. werneri. [Majure et al. 2013] [Centeno-Alvarado et al. 2022] [Simões et al. 2020]

Pollination and environmental pressure

In Catimbau National Park in Pernambuco, eight plots differing in the intensity of long-term human pressure and rainfall were studied. Pressure was assessed using a composite index including grazing, wood harvesting and human presence. A total of 240 buds were collected from 80 plants for pollen assessment. Separate comparisons used 240 flowers in each treatment, freely accessible to visitors or covered to assess spontaneous self-pollination. [Centeno-Alvarado et al. 2022]

Greater aridity and stronger pressure were associated with reductions in pollen grain number, the proportion of grains considered viable, and the pollen-to-ovule ratio. Viability was assessed by acetocarmine staining, a method based on the condition of cellular contents. Results ranged from 59,8–99,5%. Direct assessment of fertilising capacity would require an additional study of pollen germination and pollen tube growth. [Centeno-Alvarado et al. 2022]

Freely pollinated flowers set fruit more often, at 6,7–86,7% depending on the plot, than covered flowers, at 3,3–10%. At the same time, stronger human pressure correlated with more seeds per fruit, while greater aridity correlated with a higher fruit-set proportion under free pollination. Different components of reproductive success therefore responded differently. The study was a field comparison covering one observation period, which limits conclusions about the persistence of these relationships. [Centeno-Alvarado et al. 2022]

Genetics and distribution

The study of three Tacinga species included 43 plants of T. palmadora from 11 locations. Plastid markers and nuclear PhyC distinguished them from T. inamoena and T. subcylindrica. In the field, the species occupies both sandy and stony sites. Low variation in the markers studied within the species coincided with its extensive range in the Caatinga. [Barrios-Leal et al. 2024]

Climate modelling from 2024 projected a reduction in potentially suitable habitat area. For 2061–2080 under the SSP5 scenario, a decline of 26,57% was estimated in Maxent and 25,1% in BRT, assuming unlimited dispersal. The results concern climate projections from the HadGEM3-GC31-LL model. They link species distribution with environmental variables, while assessing plant survival at a specific site requires further demographic and physiological data. [Sampaio et al. 2024]