Type:— BRAZIL. Paraíba: Monteiro, Povoado Morcego, 745 m a.s.l., 7º49′50″S, 37º07′55″W, 03 January 2014, fr., Araújo s.n. (holotype EAN!).

Diagnosis:— Tacinga armata resembles T. palmadora and T. werneri from which differs by its thicker stem-segments (0.6–1.3 cm vs. up to 0.8 cm), larger (up to 5.5 cm vs. up to 2.0 cm) and thicker (1.5 mm vs. ~ 1 mm) spines, globose fruits (vs. oblongs), pericarp spines short and falling out after maturation (vs. unarmed, with densely hairy areoles), fruits attached to stem-segments for a long time after ripening (vs. immediately deciduous after maturation), and seeds 48–52 per fruit (vs. 8–38 seeds).

Description:— Terrestrial or saxicolous, erect shrub 30–80 cm tall, usually growing as isolated individuals; stemsegments oblong, 5–15 × 3.5–5.5 × 0.6–1.3 cm, erect, flat, spiny, without podaria, epidermis dark green, shoots 1–3, apical; areoles circular, 2–3 mm in diameter, disposed in 4–6 clockwise spirals, 60–108 per stem-segment (denser towards apex), hairs whitish, woolly, located in the center of the areoles, glochids golden, arranged in a crown shape around areolar hairs; spines 6–15 per areole, rigidly acicular, radial spines 5–12, 1.0– 4.5 cm long, white tipped brownish, central spines 1(–3), 1.5–5.5 cm long, longer and slightly thicker than radial ones, golden when young and gradually changing to whitish with age. Leaves subulate, 0.5–0.8 × 0.2–0.3 cm, fleshy, light green tipped reddish, early deciduous. Flowers 3.5–4.0 × 1.5–2.5 cm, apical or marginal in the distal stem-segments; pericarpel oblong, 2.0– 2.5 cm high, 1.6–2.0 cm in diameter, deeply depressed and forming an apical tube; flower bracts subtending each areole, subulate, fleshy, green, early deciduous; flower areoles disposed in 3–4 clockwise spirals, spines and hairs present; perianth triseriate, perianth segments 18 in total, tube relatively short, external perianth segments 0.7–1.0 cm long, cymbiform, fleshy, red, internal segments 1.5–2.0 cm long, oblong, erect, petaloid, apex acuminate with a terminal hair, red; stamens numerous, included, 0.5–1.0 cm long, red, surrounding the stigma lobes; anthers white (anthesis) or cream (after anthesis); stigma 6-lobed, yellowish, lobes exserted in relation to the stamens. Fruits remaining firmly attached to stem-segments after ripening; young fruits oblong, 2.5 × 1.8 cm, podaria slightly raised, funiculus 1.6 cm in diameter, 0.9–1.0 cm deep, pericarp light green, spiny, areoles with glochids and hairs, spines 1–5 per areole, 0.5–2.0 cm long, deciduous; mature fruits globose, about 3 cm in diameter, funiculus slightly depressed, pericarp dark green to pinkish (with age), mesocarp yellowish green, pulp translucent with reddish fibers. Seeds pyriform, 48–52 per fruit, two different kinds, small atrophied seeds up to 0.2 cm in diameter, large developed seeds up to 0.4 cm in diameter, tegument bony, perisperm woolly, whitish, mesosperm rigid, cream, endosperm membranaceous, brownish, embryo J-shaped, occupying all the seed cavity.

Etymology:— The specific epithet is from the Latin armatus “armed”, in reference to the size of spines and their density on the plant (including flowers and fruits).

Phenology:— On its natural habitat, flowering and fruiting were observed in December to January and September. Under cultivation, flowering occurred in October and March. These differences in flowering and fruiting could be product of the more or less constant conditions under cultivation (vs. the variable environmental conditions in nature) where, moreover, the plants have more availability of water and nutrients. Each flower remains open for two hours early in the morning (08:00 to 10:00 hr, GMT-3) and one hour late in the afternoon (16:00 to 17:00 hr). Fruits are observed approximately 15 days after anthesis and complete maturation takes at least four months. They stay firmly attached to the stem-segments for a long time after ripening.

Distribution and habitat:— Tacinga armata is known from five populations, each of approximately 2,000 individuals inhabiting areas of ca. 9,000 0 m 2. The type locality, “povoado do Morcego”, is located 8 km north of Monteiro (Paraíba, Brazil) at small isolated outcrop hills in the mountain complex known as “Serras da Jabitacá”. The other four populations are located in adjacent mountains (2 to 77 km afar from type locality) of the Serra da Bolandeira and Serra do Paulo in the Borborema Plateau. In this area, T. armata grows in full sun at 700–1100 m altitude in a xeric environment composed of compacted soils and granitic outcrops harboring shrubby caatinga vegetation (Fig. 1J–L). EMA found T. armata occurring together with T. palmadora in a mountain of the Serra da Bolandeira in Sertânia, Pernambuco (see Fig. 1K). We believe both species might occur sympatrically at other localities in these mountain ranges.

Conservation status:— According to IUCN (2019) criteria, Tacinga armata should be considered vulnerable to extinction (VU-B1a) due to its restricted geographic distribution (5 localities, EOO = 20 km 2, and AOO = 1,011.257 km 2), inhabiting areas under severe fragmentation or close to agricultural land.

Cytogenetic notes:— Tacinga armata has a 2CDNA = 6.28 pg, and a chromosome number 2 n = 66. Chromosomes are mostly metacentric and submetacentric, and relatively symmetrical. Chromosome size ranging from 1.9 to 2.2 µm. Four chromosomes have CMA + bands, two with interstitial bands and two with terminal ones (Fig. 6A). This species has a number and pattern of CMA + bands similar to those of T. werneri (2 n = 66, Alves et al. 2019) and T. lilae (2 n = 66, Majure et al. 2012). T. palmadora, the other most similar species, has a lower chromosome number (2 n = 22) and a smaller 2CDNA (2.38 pg) but similar CMA + / DPI- (2t /2i) band patterns (Alves et al. 2019).

Additional material examined: — BRAZIL. Bahia: Paraíba, São João do Tigre, início da subida para Serra do Paulo, próximo ao riacho, 890 m, 08°05′37″S, 36°39′38″W, 20 September 2020, fl., fr., Almeida 3181 (CAGD1037, EAN); Monteiro, sítio Pendurão, 720 m, 07°50′13″S, 37°07′06″W, 20 September 2020, fl., fr., Almeida 3182 (CAGD1038, EAN); Pernambuco, Poção, distrito do Quatí, 1086 m, 08°08′35″S, 36°42′03″W, 20 September 2020, fl., fr., Almeida 3172 (CAGD1028, EAN); Sertânia, Pico da Bolandeira, 1037 m, 07°58′34″S, 37°20′53″W, 21 September 2020, fl., fr., Almeida 3188 (CAGD1047, EAN).