Phytotaxa 351 (1): 001–028 http://www.mapress.com/j/pt/ Copyright © 2018 Magnolia Press Article PHYTOTAXA ISSN 1179-3155 (print edition) ISSN 1179-3163 (online edition) Accepted by Karol Marhold: 10 Apr. 2018; published: 29 May 2018 https://doi.org/10.11646/phytotaxa.351.1.1 1 The genus Odontarrhena (Brassicaceae) in Albania: Taxonomy and Nickel accumulation in a critical group of metallophytes from a major serpentine hot-spot LORENZO CECCHI 1 , ISABELLA BETTARINI 2 , ILARIA COLZI 3 , ANDREA COPPI 3 , GUILLAUME ECHEVARRIA 4 , LUIGIA PAZZAGLI 2 , AIDA BANI 5 , CRISTINA GONNELLI 3 & FEDERICO SELVI 6* 1 Natural History Museum, Botanical Section “Filippo Parlatore”, University of Florence, via G. La Pira 4, I-50121 Firenze, Italy 2 Department of Experimental and Clinical Biomedical Sciences and Biochemistry “Mario Serio”, University of Florence, viale G.B.Morgagni 50, 50134 Firenze, Italy 3 Department of Biology, University of Florence, via P. A. Micheli 1, I-50121 Firenze, Italy 4 Laboratoire Sols et Environnement, Nancy-Université, INRA, 2 avenue de la Forêt de Haye, B.P. 172 F-54505, Vandoeuvre-lès-Nancy, France 5 Agro-Environmental Department, Faculty of Agronomy and Environment, Agricultural University of Tirana, Koder-Kamez, Tirana, Albania 6 Department of Agrifood Production and Environmental Sciences, University of Florence, P.le delle Cascine 28, 50144 Firenze, Italy *corresponding author: federico.selvi@unifi.it ABSTRACT Metal hyperaccumulator plants represent a unique biological resource for scientific research and practical applications. Though essential, however, an adequate knowledge of the systematics of these plants is often missing. This is the case of Odontarrhena, a large but taxonomically critical group of nickel hyperaccumulators from Eurasia. We present a study on this genus in Albania, to fill a gap in our knowledge of this group from a major centre of diversity of metallicolous flora, and to contribute updated information to the Global Hyperaccumulator Database. Morphological and karyological analyses of material from field collections across all major serpentine outcrops in the country, in different years and seasons, allowed to delimit seven taxa: O. albiflora, O. chalcidica, O. moravensis, O. sibirica, O. decipiens, O. smolikana subsp. glabra and O. rigida. The three latter taxa have been long neglected and were resurrected in view of their clear distinctness, while com- monly accepted taxa such as O. bertolonii subsp. scutarina and O. markgrafii were reduced to synonymy of O. chalcidica due to the lack of consistent differentiation. Polyploidy was prevalent, while diploid complements were typical of the two vicariant endemics O. rigida and O. moravensis. Types are indicated or newly designated for each entity, and nomenclatural issues are addressed based on in-depth studies of literature and herbarium material. Revised descriptions, phenology, habitat and distribution data are given for each taxon, as well as original iconographies and chromosome counts. A revised identifi- cation key is provided. Shoot nickel concentrations were determined to assess accumulation levels of taxa and populations in natural conditions and their potential for phytoextraction of this metal from the soil. With ca. 23000 and 17000 μg of Ni g -1 of shoot dry weight, respectively, the tetraploids O. chalcidica and O. decipiens were the most promising candidates, especially the latter for its robust habit. Keywords: Albanian flora, Alyssum s.l., Balkan endemics, Ni-hyperaccumulators, serpentine plants, systematics INTRODUCTION Plants that are adapted to live on metal-enriched soils and able to survive and reproduce there without suffering from toxicity are termed ‘metallophytes’ (Baker et al. 2010, Wójcik et al. 2017). Several categories can be distinguished based on whether these plants are restricted to metal-rich soils (obligate) or not (facultative), or the type of metal they are able to cope with. An even more outstanding specialization shown by some hundreds of angiosperms is their ability to accumulate heavy metals in concentrations well above those found in the soil, that is called hyperaccumulation. The largest group of hyperaccumulators is that of the Nickel specialists (Global Hyperaccumulator Database; http:// hyperaccumulators.smi.uq.edu.au/collection/), which exploit the high levels of this metal naturally found in the ultramafic rocks (Brooks 1980). In the above-ground parts of these species there are Ni concentrations of at least 1000 μg g -1 shoot dry weight, and this is interpreted as a defensive strategy against natural enemies due to toxic or repellent