Opuntioids of eastern Brazil—Tacinga, Quiabentia, Brasiliopuntia

Sabrina Mota Lambert & Root Gorelick

Root Gorelick and Sabrina Lambert covered the prickly pear genera of eastern Brazil in a series of articles in our special issue, Root, with short introductions to Quiabentia and Brasiliopuntia, Sabrina with an in-depth overview of the hummingbird-pollinated Tacinga.

Quiabentia

Quiabentia is the sister genus to Pereskiopsis, belonging in the clade containing North American cylindrical stemmed members of the subfamily. Q. verticillata grows at least 2000 km from Q. zehntneri, the former in western Paraguay and nearby portions of Bolivia and Argentina, the latter endemic to Bahía and Minas Gerais, Brazil. Q. verticillata is a large tree, while the Brazilian Q. zehntneri is a small shrub to two or three meters tall, resembling its close relative Perskiopsis. While we only saw Q. zehntneri on limestone outcrops, apparently it can also be found under other edaphic conditions.

Brasiliopuntia

The monotypic genus Brasiliopuntia is the sister genus to Tacinga, but not the vegetatively similar North American genus Nopalea. Brasiliopuntia brasiliensis has bee-pollinated, bowl-shaped flowers with yellow or greenish-yellow petals, quite unlike the hummingbird-pollinated flowers of Nopalea and Tacinga. Growing at the periphery of dense forests, it starts off with a fast growing cylindrical trunk from which originate flat pads and occassional cylindrical branches. The trunk bolts vertically toward the canopy to escape the shade of its non-cactus compatriots, a race that may make Brasiliopuntia, at 20–25 m, the tallest freestanding cactus. Neverthless, plants growing even a few meters inside of a forest are notoriously difficult to find, even with their vibrant red fruits.

Tacinga

The genus Tacinga belongs to the subfamily Opuntioideae of Cactaceae, where it is placed in tribe Opuntieae. Tacinga was first described in 1919 by Britton and Rose, who distinguished the genus from Opuntia and Nopalea by the reflexed, green perianth segments, presence of staminoids between the stamens and perianth segments, cylindrical stems, and because Tacinga had a scrambling or scandent liana-like (vine-like) habit not found in other opuntioids. Tacinga shares with Nopalea the possession of erect stamens which are insensitive to touch, unlike Opuntia where the stamens are sensitive. Several subsequently described taxa (T. zehntneri, T. atropurpurea and its variety zehntnerioides) are now considered synonyms of Britton and Rose’s original species.

In 2002 the genus was expanded to include a number of species endemic to eastern Brazil that had previously been allied with Opuntia. These species differed from Tacinga in their shrubby rather than liana-like habit, and because they possessed flattened, oblong to orbicular cladodes (stems), instead of the long cylindrical stems typical of Tacinga.

Tacinga can be divided in three species-groups based on morphology. In the first species-group (T. funalis and T. braunii), T. funalis is the species with the widest distribution, occurring in Pernambuco and Bahia and growing in areas of the caatinga vegetation. It has characteristic, long cylindrical cladodes. Tacinga braunii has an allopatric distribution relative to T. funalis, restricted to the northeastern region of Minas Gerais in the valley of the river Jequitinhonha, where it grows on gneiss or granite rock outcrops.

The second species-group comprises T. palmadora and T. werneri, species with very similar morphology and easy to misidentify if only vegetative material is examined. They are distinguished by their flowers and fruits. T. werneri has staminodes in the flowers and larger, whitish, ovoid fruits with a pinkish pulp when ripe. T. palmadora has smaller clavate (club-shaped) fruits, greenish or reddish to purplish when ripe with a translucent pulp. Tacinga palmadora has a wide distribution, occurring on rock outcrops or in the soils of the caatinga in the states of Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe and Bahia; T. werneri occur in the same kinds of environment than T. palmadora, but it has a more restricted distribution, occurring in Bahia and northeast of Minas Gerais. The distribution of T. werneri in Bahia overlaps with that of T. palmadora, and the two species can be found growign together, for instance, in the region of Morro do Chapéu, Bahia.

The third group includes T. inamoena and T. saxatilis, distinguished from the remaining tacingas by their low, subshrub habit and round to oblong pads. Tacinga saxatilis grows in caatinga and cerrado vegetation of western Bahia and northwestern Minas Gerais, where it is restricted to limestone rock outcrops. Tacinga saxatilis can be distinguished from T. inamoena by its spiny areoles (T. inamoena lacks spines) and different flower and fruit morphology. The distribution of T. saxatilis is largely parapatric relative to that of T. inamoena, with both species growing together in a few localities and sometimes hybridizing. T. inamoena has the widest distribution of the genus, occurring in all states of northeastern Brazil and also in the north of Minas Gerais, a distribution that corresponds closely to the limits of the caatinga biome. Within this area T. inamoena occurs in many diverse environments, growing in the varied soils of the caatinga and also on outcrops of a range of rock types: gneiss, granite, quartzite, sandstone, and limestone. It also occurs in high-altitude campo rupestre vegetation, rock outcrops, and in sandy soils and includes disjunct populations growing on sandstone rock outcrops in the cerrado vegetation of western Bahia and in areas transitional between the semiarid caatinga vegetation and the humid Atlantic Forest vegetation of eastern Bahia (these corresponding to T. inamoena ssp subcylindrica). Despite being easily recognizable, T. inamoena displays a large amount of morphological variability among its populations.

Tacingas are primarily pollinated by hummingbirds, which are surprisingly territorial animals that guard their food sources. Therefore, Tacinga gene flow is quite limited geographically, which results in strong isolation of populations. This effect helps to maintain the historical influences of climate and geography on their distribution by preventing the effects to be washed out by extensive gene flow. It is thought that seeds don’t travel far, for while the seed dispersers of Tacinga seeds are not known, they are assumed to be lizards and small mammals.