Machaerophorus arequipa Al-Shehbaz, A. Cano, M. Cueva & Salariato, 2018

Al-Shehbaz, Ihsan A., Cano, Asunción, Manchego, Marco Antonio Cueva & Salariato, Diego L., 2018, Remarkable discoveries in the long-neglected and Peruvian-endemic genus Machaerophorus (Brassicaceae), Phytotaxa 360 (2), pp. 114-124 : 116-118

Machaerophorus arequipa Al-Shehbaz, A. Cano, M. Cueva & Salariato , sp. nov.

Diagnosis:— Macharophorous arequipa is readily distinguished from the other two species of the genus by having white flowers and terete, torulose fruit.

Type:— PERU. Arequipa: Prov. Arequipa, Dist. Uchumayo, Quebrada Tinajones-Cerro Verde Ladera rocosa suelo arenoso entre rocas, 16°29 ʹ 56.36 ʺ S, 71°37 ʹ 57 ʺ W, 2428 m, 29 August 2012, M. Cueva & C. Dávalos M. 1925 (holotype USM-302012!; isotypes HUSA!, MO-6701111!, SI!). Figures 1 , 2 , 5C , 6 .

Description: —Herbs suffrutescent perennials or subshrubs, not glaucous, somewhat canescent, floccose-arachnoid on young parts, puberulent to glabrescent with age. Stems woody on lowermost branches, those of current-year growth herbaceous, 40–62 cm tall, erect to ascending, branched, usually densely floccose at and above nodes, becoming puberulent and eventually glabrescent on older parts. Cauline leaves 4–7 cm long, adaxially grooved; petiole 0.5–2.2 cm long, floccose at least adaxially within groove, usually sparsely puberulent abaxially; lateral leaf lobes 3–6 on each side, 1–3 cm × 0.5–0.8 mm, entire, gradually reduced in length upwards; terminal leaf lobe about as long as or shorter than lateral lobes. Racemes 10–40-flowered; rachis puberulent; lower and middle fruiting pedicels divaricate-ascending, 12–26 mm long, straight or slightly incurved, sometimes secund, usually moderately puberulent at axils, sparsely so elsewhere. Sepals 10–12 mm long, puberulent, green and with whitish margin; petals white to creamy white, greenish white abaxially, 20–26 mm long; blade oblong to ovate, 5–8 × 2.5–3 mm, obtuse; claw 14–16 mm long; filaments white, 10–14 mm long; anthers 3.5–4 mm long; ovules 38–50 per ovary. Fruit linear, cylindrical, 3–4 cm × 1.5–2 mm, torulose, terete, straight or slightly curved, attenuate to style, sessile or on a minute gynophore to 0.5 mm long; valves glabrous or sparsely puberulent; style 1–2.5 mm long. Seeds uniseriate, brown, ovate, compressed, margined, 1.2–1.3 × 0.7–0.9 mm.

Distribution: —Endemic to the Peruvian Department Arequipa.

Etymology: —The species epithet arequipa , which is named after the Peruvian department Arequipa, is a noun used in apposition and, therefore, should be maintained according to Article 23.5 of the International Code of Nomenclature for Algae, Fungi and Plants ( McNeill et al., 2012).

Additional specimens examined (paratypes): — PERU. Arequipa: Prov. Arequipa, Dist. Uchumayo, Quebrada Tinajones-Cerro Verde Ladera rocosa Suelo arenoso entre rocas, 16°29 ʹ 59.38 ʺ S, 71°37 ʹ 52 ʺ W, 2441 m, 10 August 2012, M. Cueva & C. Dávalos M. 1918 (MO-6701113, MO-6701114!, USM) ; same area, 16°29 ʹ 45.2 ʺ S, 71°37 ʹ 58.26 ʺ W, 2407 m, 11 February 2013, M. Cueva, C. Dávalos M. & L. Mosaurieta 1933 (MO-6701112, USM) .

Habitat: — Machaerophours arequipa grows in arid zones with sparse desert scrub and is restricted to shady habitats in valley bottoms and rocky or rocky-sandy slopes at about 2400 m. The main vegetation components are Ephedra americana Humb. & Bonpl. ex Willdenow (1806: 860) , Senecio yurensis Rusby (1912: 133) , Cumulopuntia sphaerica ( Foerster 1861: 167) E.F. Anderson (1999: 324) , Tiquilia elongata ( Rusby 1920: 107) A.T. Richardson (1976: 236) , Ambrosia artemisioides Meyen & Walp. in Meyen (1843: 268), and columnar cacti such as Browningia candelaris ( Meyen 1834: 447) Britton & Rose (1920: 63) , Neoraimondia arequipensis ( Meyen 1834: 41) Backeberg (1937: 1) , and Weberbauerocereus weberbaueri (K. Schum. ex Vaupel 1913: 22) Backeberg (1956: 27) . According to Zamora (1996) and Leon et al (2006) the habitat of this species corresponds to Desert Scrub Region of the western slopes of the Andes, between 1000 and 2500 m.

Discussion: —Unlike the following two species, Machaerophorus arequipa does not seem to be closely allied to either of them. It drastically differs from its congeners by having white flowers, uniseriate seeds, and terete, torulose fruit.

Figures

FIGURE 1. Machaerophorus arequipa. A. Plants. B. Flower. C. Fruit and fruiting pedicel. Drawn by Al-Shehbaz from paratype (MO 6701113).

FIGURE 2. Machaerophorus arequipa. A. Plants. B. Older stem and leaves. C. Young stem and leaves showon indumentum. D. Flower top view. E. Flower lateral view. F. Portion of infructescence. Photos by M. Cueva.

FIGURE 5. Fruit of Machaerophorus. A. M. mathioloides. B. M. laticarpus. C. M. arequipa. Drawn by Al-Shehbaz. A from isotype (P 00730030), B from isotype (MO 6832092), C from paratype (MO 6701113).

FIGURE 6. Distribution map of Machaerophorus arequipa (circle) and M. laticarpus (triangle).