Tetragonia L .

Manning, John & Klak, Cornelia, 2022, New infrageneric taxa in Leucospermum (Proteaceae) and Tetragonia L. (Aizoaceae) and a new name in Aizoon subgenus Galenia (Aizoaceae) in southern Africa, Bothalia (a 11) 52 (1), pp. 1-5 : 2-3

2. Tetragonia L. ( Aizoaceae : Aizooideae)

Tetragonia L. ( Aizoaceae : Azooideae) as recently re­circumscribed, is a genus of ± 50 species from temperate and subtropical regions, mainly in the southern Hemisphere ( Klak et al. 2017). The southern African taxa were last revised by Adamson (1955), and this remains the current treatment for the species in the region. In his classification, Adamson (1955) segregated the species among the four subgenera Tetragonia, Tetragonoides DC. , Anisostigma (Schinz) Engl. and Tribulocarpus (S.Moore) Adamson , defined by several characters of the fruits and flowers. The recent molecular phylogenetic analysis of the subfamily by Klak et al. (2017), however, uncovered some unexpected relationships among the species that necessitated realignments among several taxa in order to render them monophyletic. Among these was the removal of Tetragonia subgenus Anisostigma and subgenus Tribulocarpus to the new tribe Anisostigmateae Klak in subfamily Sesuvioideae as the genera Anisostigma Schinz and Tribulocarpus S.Moore respectively.

In addition to these changes, the circumscription of Tetragonia subgenus Tetragonoides was greatly altered by the removal from it of most of the southern African taxa previously included there by Adamson (1955). Tetragonia subgenus Tetragonoides is now understood to be essentially Australasian in distribution, with the exception of the cosmopolitan littoral species T. tetragonoides (Pall.) Kuntze , the type of the subgenus. Two additional subgenera, subgenus Tetragonella (Miq.) Klak and subgenus Americanae Klak were established to accommodate respectively the other Australasian and the American species ( Klak et al. 2017).

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The remaining four southern African species that were included by Adamson (1955) in subgenus Tetragonoides were retrieved by Klak et al. (2017) as a clade sister to subgenus Tetragonia and were accordingly included in it, with the observation that the ‘series erected by Adamson (1955) should be maintained’. This alludes to the seven sections recognised by Adamson (1955) in subgenus Tetragonia . Although they included these additional four former members of subgenus Tetragonoides in subgenus Tetragonia, Klak et al. (2017) did not accommodate them within the existing classification.

Significantly, the removal of T. tetragonoides from this group renders it morphologically more homogenous. The four species share a prostrate, ± annual habit and half­inferior ovary, and differ from all other members of subgenus Tetragonia in having the stamens less than twice as many as the perianth segments vs. more than twice as many as the perianth segments (Adamson 1955). The new series Echinatae J.C.Manning & Klak is accordingly proposed here to accommodate them.

There are two other nomenclatural corrections required in subgenus Tetragonia . The first concerns the authorities for the infrageneric names that were published by Fenzl (1862). Adamson (1955) treats these as series, with Fenzl (1862) as author. However, examination of Fenzl (1862) reveals that they were published as third tier names two ranks below sectional level but without a definite rank. Although they are to be accepted as validly published by Fenzl (1862) they are to be treated as unranked (Turland et al. 2018: ‘Art. 37.3. A name published before 1 January 1953 without a clear indication of its rank is validly published provided that all other requirements for valid publication are fulfilled; it is, however, inoperative in questions of priority except for homonymy. If it is the name of a new taxon, it may serve as a basionym or replaced synonym for subsequent new combinations, names at new ranks, or replacement names at definite ranks. ’). Their later publication by Adamson (1955) with a clear indication of the rank of series serves as the first publication at that rank and they are therefore to be treated as combinations by Adamson (1955).

The second correction concerns the status of the series that includes the type of the genus, T. fruticosa L. Although the genus Tetragonia was only lectotypified by Britton (1918) after the treatment by Fenzl (1862), the name T. [unranked] Fruticulosae Fenzl. (1862) is to be treated as not validly published [Turland et al. 2018: ‘Art. 22.2. A name of a subdivision of a genus that includes the type (i.e. the original type or all elements eligible as type or the previously designated type) of the adopted, legitimate name of the genus is not validly published unless its epithet repeats the generic name unaltered. For the purposes of this provision, explicit indication that the nomenclaturally typical element is included is considered as equivalent to inclusion of the type, whether or not it has been previously designated. ’]. Similarly, the publication of this taxon at series rank (spelled Fruticosae) by Adamson (1955) is to be treated as not validly published. The correct name for this taxon is series Tetragonia (Turland et al. 2018: ‘Art. 22.1. The name of any subdivision of a genus that includes the type of the adopted, legitimate name of the genus to which it is assigned is to repeat that generic name unaltered as its epithet, not followed by an author citation. ’).

The species of Tetragonia subgenus Tetragonia are thus distributed among eight series as follows:

Tetragonia L. ,

Species plantarum 1: 480 (1753).

Type: T. fruticosa L. , lecto., designated by Britton, Flora of Bermuda: 125 (1918).