Discocactus petr-halfarii, 2015

Santos, Marianna Rodrigues, Machado, Marlon Câmara, Garcia, Flávia C. P. & Taylor, Nigel P., 2015, Taxonomic adjustments in Discocactus (Cactaceae), Phytotaxa 207 (2), pp. 209-212 : 209-211

1. Discocactus zehntneri subsp. petr-halfarii (M.Zachar) M.R.Santos & M.C.Machado , comb. nov. ( Fig. 1 ).

Bas.: Discocactus petr-halfarii M. Zachar (2008:43) , originally “ Discocactus petr-halfari ”). Type: — BRAZIL. Bahia, Mun. Juazeiro, 03 March 2007, Zachar s.n. (holotype UFG!).

≡ Discocactus bahiensis subsp. petr-halfarii (M.Zachar) Braun & Eddie Esteves Pereira (2008: 184) .

Description:— Plants depressed-globose to globose. Roots slightly branched, taproot thickened. Stem 4–5 × 2–15 cm, green. Ribs 10–14, broken into rounded tubercles. Visible areoles 2–5 per rib, oval to elliptic, 0.5–1.4 × 0.4 mm, not sunken, with much beige to white indumentum. Spines grey to yellow, the radial ones 7–12, 10–25 × 1.5 mm, arranged in c. 3 pairs on each side; central spine absent. Cephalium 0.6–2.0 × 2.6–3 cm, with white to greyish wool; bristles little or absent. Flower funnel-shaped, 34–36 × 23–26 mm, white, naked, perianth-segments with ciliate margins, sweetly scented; receptacle-tube bract-scales 2–8 × 0.5–4.0 mm, cream to white, apex acuminate to acute; inner perianth-segments 15–22 × 3–6 mm, white lanceolate to spathulate, acute to cuspidate; outer perianth-segments 10–24 × 4–6 mm, lanceolate to spathulate, acute, cream to white; style 12–18 mm long, stigma-lobes 5, 3–4 mm long; stamens 1–2 mm long. Fruit 35 × 5 mm, pink to reddish, with remains of perianth. Seeds about 100 seeds per fruit, helmet-shaped or more elongated, c. 1 × 1 mm, testa with small to elongate tubercles.

Habitat and Distribution:— Endemic to Brazil in locality Bahia, Mun. Juazeiro (“Caatinga”), on stony clay soil at an altitude of 350– 550 m.

Flowering and fruting time:— Flowering between November to March; fruits can be found until June.

IUCN Red List Category:— Discocactus zehntneri subsp. petr-halfarii is only known from a single population (according to IUCN 2010, with EOO <100 km 2, AOO <10 km 2) and in January 2015, only 1945 individuals among seedlings and plants in reproductive age were found in nature (M.V. Meiado and J.P.B. Nascimento, pers. comm.). This population is located beside a road that has recently been expanded and paved (Gerardus Olsthoorn, 11 November 2014, pers. comm.), resulting in the destruction of more than 50% of the population. In addition, the natural habitat of the species is surrounded by cropland and runs the risk of being converted into a cultivated area in the near future, which will result in the extinction of the subspecies in the wild. We here propose for Discocactus zehntneri subsp. petr-halfarii the category “Critically Endangered” (CR) on the basis of the criteria A2 (a,c), A3(c), B1ab (ii,iii,v), B2ab (ii,iii,v).

Notes:— Discocactus petr-halfarii Zachar (2008: 43) was treated in the past as a synonym or subspecies of D. bahiensis (see e.g., Braun & Esteves 2008: 184), while it is here proposed as a subspecies of D. zehntneri . In fact, our phylogenetic study of the genus Discocactus shows that D. petr-halfarii is grouped with D. zehntneri s.str. with a good bootstrap support and high posterior probability in the parsimony and bayesian analyses respectively ( Santos et al. 2013). From the morphological point of view, it differs from D. zehntneri s.str. in having a globose plant body and ribs with globular tubercles, while it is differentiated from the other subspecies mainly due to central spines being absent, radial spines curved, well developed areoles and presence of a thickened taproot ( Fig. 2 ).

Specimens examined:— BRAZIL. Bahia: Juazeiro , 4 March 2007, Zachar, M. ( UFG) ; Frade, 26 km of Juazeiro in BR-235, 03 December 2011, Meiado et al. 750 ( HVASF, VIC) .

2. Discocactus heptacanthus (Barbosa Rodrigues) Britton & Rose (1922: 218) . Bas.: Malacocarpus heptacanthus Barbosa Rodrigues (1898: 29) .

Lectotype (designated in Taylor & Zappi, 2004: 446): — [Icon] tab. 11 in Barbosa Rodrigues (1898).

= Discocactus lindanus Diers & Esteves Pereira (1981: 56 originally as “ Discocactus lindaianus ”), syn. nov.

Type: — BRAZIL: Goiás, E to NE region of the state of Goiás, 1973, Esteves Pereira 9 (holotype UFG!).

Notes:— According to Hunt et al. (2006: 76), D. lindanus can be considered a synonym of D. diersianus . On the basis of the phylogenetic study by Santos et al. (2013), D. diersianus is grouped with D. heptacanthus and morphological characters also indicate this proximity, such as the flattened tubercles and the style exceeding the corolla aperture.

Figures

FIGURE 1. A−B) Habit showing stem, rib shape and areole morphology of Discocactus zehntneri subsp. petr-halfarii. C) Longitudinal section of flower and perianth-segments. D) Stigma-lobes. E) Stamen. F) Seed. Drawn by Reinaldo Pinto.

FIGURE 2. Pictures showing morphologic differences among subspecies of D.zehntneri. A) D.zehntneri subsp.zehntneri. B) D. zehntneri subsp. boomianus. C) D. zehntneri subsp. petr-halfarii. D) D. zehntneri subsp. petr-halfarii in flower. Photographs by M. Teles (A), M. C. Machado (B), G. Olsthoorn (C−D).