Typification and taxonomy in Mimosa subser. Obstrigosae (Fabaceae, mimosoid clade)

Abstract: During a revision of Mimosa sect. Mimosa from southern Brazil, we noticed that M. adpressa Hook. & Arn., a species of M. subser. Obstrigosae (Benth.) Barneby, has never been typified and that M. subinermis Benth. has long been considered a synonym of M. rupestris Benth. We designate here a specimen from Argentina, collected by Tweedie and deposited in the Kew herbarium, as the lectotype of M. adpressa. Furthermore, we show that M. subinermis is readily distinguished from M. rupestris by many morphological features (e.g. habit, calyx type, fruits), supporting our hypothesis that M. subinermis is a distinct species. Citation: Schmidt Silveira F., Sfoggia Miotto S. T. & Vieira Iganci J. R. 2018: Typification and taxonomy in Mimosa subser. Obstrigosae (Fabaceae, mimosoid clade). – Willdenowia 48: 443–449. doi: https://doi.org/10.3372/wi.48.48314 Version of record first published online on 28 November 2018 ahead of inclusion in December 2018 issue.

One reason for this complex taxonomy is that many of the species are very similar in their vegetative phase, and it is sometimes necessary to examine the fruits to provide an accurate identification. Secondly, hybridization may occur between some species of M. subser. Obstrigosae, making it difficult to establish diagnostic characters, such as was shown in other subseries of M. sect. Mimosa ser. Mimosa, e.g. M. subser. Brevipedes (Morales & al. 2014) and M. subser. Mimosa (Morales & Fortunato 2010). Moreover, distinct species are sometimes treated as synonyms. For example, M. adpressa Hook. & Arn. (Hooker & Arnott 1833: 202) and M. obstrigosa Burkart (1946: 231) are commonly misidentified and have been mistakenly considered to be synonyms (e.g. by The Plant List 2013), and M. subinermis Benth. has long been considered a synonym of M. rupestris Benth. (Bentham 1875;Barneby 1991).
The difficulties of delimitation among species favours taxonomic confusion, which can lead to over-or underestimating species richness (Ely & al. 2017). In this context, typification plays an important role, in assigning the correct application of a name. If species names are used without knowledge of their status (e.g. accepted, synonyms, doubtful), this can have negative consequences in fields such as conservation biology and ecology (Dayrat 2011). Therefore, the aims of our study were: (1) to lectotypify Mimosa adpressa and (2) to demonstrate that M. subiner mis is a species distinct from M. rupestris.

Material and methods
For the typification of Mimosa adpressa, we examined specimens deposited in K, E and TCD (herbarium codes according to Thiers 2018+). To corroborate that M. sub inermis should be considered a species distinct from M. rupestris, we studied type material in K, P and TUB and consulted other material from southern Brazil and Uruguay in FLOR, FURB, HAS, HDCF, HUCS, ICN, MBM, MVFA, MVJB, MVM, PACA, PEL and SMDB. Furthermore, we conducted field trips to confirm the distribution of M. subinermis and to provide more morphological evidence to distinguish this species. Typification -According to Art. 9.6 of the International Code of Nomenclature for algae, fungi, and plants (Turland & al. 2018), a syntype is any specimen cited in the protologue when there is no holotype, or any one of two or more specimens simultaneously designated in the protologue as types; and reference to an entire gathering is considered as citation of the included specimens. In the protologue of Mimosa adpressa, Hooker & Arnott (1833: 202) cited two gatherings from Argentina ("Entre Rios, Tweedie") and Uruguay ("Uraguay, Baird"). Specimens belonging to these gatherings are therefore syntypes. Barneby (1991) mentioned the existence of syntypes both in K and E. We found three specimens of the Tweedie gathering in K (barcodes K000532824, K000556935 and K000556936) and one specimen of the Baird gathering sharing its barcode (K000543690) with a fourth specimen of the Tweedie gathering. We found two further specimens of the Tweedie gathering in E (barcode E00514885) and TCD (barcode TCD0004716).

Results and Discussion
Among these syntypes, we consider the most appropriate choice of lectotype to be the Tweedie specimen in K with barcode K000532824. This specimen clearly shows the main morphological feature identifying it as Mimosa adpressa, i.e. sessile or subsessile inflorescen ces. Furthermore, the label is clear and the sheet bears only material of M. adpressa. The lectotype excludes the stem on the upper left side of the sheet, which is annotated as a specimen from a different gathering (Maldonado, Capt. King s.n., barcode K000532823). At least one of the other syntypes of M. adpressa could lead to misinterpretation if selected as the lectotype. For example, the sheet in K bearing the Baird specimen (barcode K000543690) also bears a duplicate of the Tweedie specimen, as well as a fragment annotated in pencil as M. bonplandii Benth., but without further annotation or labels, all mounted on the same sheet and sharing the same barcode. We also have some doubts about the syntype status of two of the sheets in K: that with the barcode K000556935 appears to bear the date "1837" on its label, i.e. later than the protologue, and the sheet with barcode K000556936 could bear material from two different gatherings, according to the handwritten field notes on two of the labels.
Phenology -Flowering from autumn to spring; fruiting from autumn to the beginning of summer (Izaguirre & Beyhaut 2003).
Phenology -Flowering from February to May; fruiting during November and December.
Distribution and ecology -Brazil, State of Rio Grande do Sul: Serra do Sudeste in Caçapava do Sul and Santana da Boa Vista. The species grows on sandstone outcrops, in rocky grasslands and in association with forest on outcrops.
Conservation status -This species lacks information about distribution, ecology and threats because there are few records and most of them have inaccurate geographic data (absence of geographic coordinates). Almost all the excursions we undertook to delimit its distribution failed to find the species at the localities of early records. We found only one locality, but with no more than five individuals. In that regard, Mimosa subinermis was evaluated as Data Deficient (DD) according to IUCN categories and criteria (IUCN 2012(IUCN , 2016. Remarks -The name Mimosa subinermis has been considered a synonym of M. rupestris, but we consider it to be a distinct species, and it is therefore reinstated here after 143 years. Mimosa subinermis and M. rupestris were first described by Bentham (1841: 385), both from Sellow collections and both on the same page of Bentham's treatment. In the protologue of M. rupestris, it was cited from the State of Rio Grande do Sul in southern Brazil ("Brazil, Sello; Mountains of Rio Jaquhy, Tweedie"), whereas M. subinermis was only generally cited as a Brazilian species ("Brazil, Sello"), without any finer detail about locality of occurrence. The major differences between the two species according to Bentham (1841) were: absence/presence of aculei, the relation of peduncle length to pinna length, leaflet morphology, and calyx length.
Years later, however, Bentham (1875) appeared to have been less certain about those differences and considered Mimosa subinermis to be a synonym of M. rupestris. Bentham clearly also had difficulty distinguishing other taxa of M. subser. Obstrigosae. For example, M. ouro brancoensis (Burkart 1947), from Minas Gerais State, Brazil, was not described until a century after Bentham (1841) published M. rupestris and M. subinermis, even though Bentham had access to material of M. ourobran coensis. Bentham cited these early collections of M. ourobrancoensis as M. rupestris in Flora brasiliensis (Bentham 1876). Barneby (1991: 616) also agreed with the synonymization by Bentham (1875) of Mimosa subinermis under M. rupestris, remarking that "M. subinermis, which Bentham himself eventually treated as a taxonomically negligible armed variant of M. rupestris, is the only specimen of its sort known to me. Except for its very few aculei, inserted on one infrastipular rib immediately below random nodes, it appears identical with genuine M. rupestris. Nothing exact is known of its origin or dispersal, and its status remains contingent on rediscovery." However, here we show that Mimosa subinermis is readily distinguished from M. rupestris by its habit, presence of aculei, branches sparsely covered by strigose trichomes, paleaceous calyx covering almost half of the corolla length, and fruits covered by strigose adpressed trichomes (Fig. 2, Table 1).