Full name and orig. publication: Tetraphyllum Griff. ex C.B.Clarke, in A. & C. DC, Monogr. Phan. 5(1): 136 (July 1883; Gesneriaceae), nom. cons. (against Tetraphylloides Hosius & von der Marck, Palaeontographica 26: 137, 1880), name based on Griff., Not. Pl. Asiat. 4: 148 (1854), nom. nud.

Etymology: From the Greek τετρα, tetra = four, and φυλλον, phyllon = leaf, alluding to the conspicuous tetramerous leaf whorl at the top of the plant.

Synonyms: Tetraphylloides Doweld (2017).

Infrafamilial position: Didymocarpoideae-Trichosporeae-Tetraphyllinae (Weber et al. 2013).

Description: Terrestrial, perrenial herbs with (lignescent?) monocarpic stem(s). Stem erect, caulescent, with tawny villose indumentum, bearing a tetramerous (pseudo-) whorl or a leaf pair at the top, and pairs of scale leaves (in some species with axillary inflorescences) along the stem. Leaves petiolate or (sub)sessile, ovate or lanceolate, partly unequal-sided. Cymes axillary, condensed, flowers nearly sessile; bracteoles small. Sepals 5, almost free to base. Corolla widely funnel-shaped, limb bilabiate to subregular, lobes obtuse. Stamens 4, didynamous, or 2, filaments emerging near corolla base, anthers coherent at the tips, opening by longitudinal slits. Nectary much reduced. Ovary ovoid, style slender, stigma obscurely bilobed. Capsule splitting loculicidally and septicidally into 4 valves, leaving the two main ribs united to the style and 4 papery enrolled placentae.

Chromosome number: Unknown.

Species number: 3.

Type species: Tetraphyllum bengalense C.B.Clarke.

Species names: (1) Tetraphyllum bengalense C.B.Clarke, (2) T. confertiflorum (Drake) B.L.Burtt, (3) T. roseum Stapf.

Distribution: NE India, Bangladesh, Burma, Thailand.

Ecology: Damp rocks in forest.

Notes:
(1) Originally (Griffith 1854: 148), the name Tetraphyllum was instated as a "temporary name referring to undescribed genera in the collection of the author" and neither a description nor species name(s) or specimen(s) were cited. Griffith’s name has therefore to be treated as a nomen nudum. Validation of the name was almost 30 years later, by C.B.Clarke (1883). A different view is held by IPNI: Here Griffith is considered as the valid authority and Clarke’s name as illegitimate.
(2) The name Tetraphyllum was recently replaced by Tetraphylloides Doweld and the three species recognised in Tetraphyllum were transferred to Tetraphylloides (Doweld 2017). The reason for the replacement is that Doweld (2017) discovered that the latter name was antedated by the name of a fossil, Tetraphyllum Hosius & von der Marck (1880). Hosius & von der Marck (1880) and Doweld (2017) considered the fossil to be a plant fossil ("Plantae incertae sedis"), but Bertling (2019) provided evidence that the fossil was a trace fossil of a fish and qualified Doweld’s names as illegitimate. However, as the fossil was considered as a plant at the time of its publication, Tetraphyllum Griff. ex C.B.Clarke must be treated as a later homonym and Doweld’s replacement of Tetraphyllum by Tetraphylloides was formally correct (see ICN Art. 54.1(a)).
(3) However, Middleton et al. (2021) submitted a proposal to conserve the name Tetraphyllum over Tetraphylloides. The proposal successfully passed the Nomenclature Committee for Vascular Plants (Applequist 2024) and the General Committee (Wilson 2024) and thus fulfills the requirements for ratification at the next International Botanical Congress (2029, Cape Town, South Africa). As this will be only a final formality, we use the traditional name Tetraphyllum.
(4) (Both the habit and the peculiar capsular fruit (with persistent style base holding the main ribs of the two carpels together after the four valves have fallen) are unmistakable.
(5) The genus represents another case of the transition from tetrandry (T. roseum) to diandry (T. bengalense, T. confertiflorum).

Selected references: Burtt, Thai Forest Bull. (Botany) 29: 81-109 (2001), annot. checklist Gesneriaceae (Thailand); Doweld, Phytotaxa 329(3): 293-295 (2017), replacement names; Hosius & von der Marck (Palaeontographica 26: 137-138 (1880), descr. fossil Tetraphyllum; Bertling, Phytotaxa 425: 63–66 (2019), trace fossil; Applequist, Taxon 73(1): 288-304 (2024); Wilson, Taxon 73(4): 1081-1084 (2024).

Tax. details, cytology, and bibliography: Gesneriaceae Resource Centre (GRC). Royal Botanic Garden Edinburgh.

Page content and update responsibility/contact: David J. Middleton.
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