|Tiganophyton karasense Swanepoel, F.Forest & A.E.van Wyk|
in Swanepoel, Chase, Christenhusz, ... et van Wyk, 2020.
Photos: W. Swanepoel, Art work: Daleen Roodt.
Tiganophyton karasense, an evergreen dwarf shrub, is described as a new species. A new genus and family are also proposed for it in the order Brassicales. Phylogenetic analysis of DNA sequence data indicate that Tiganophyton is sister to Bataceae/Salvadoraceae, and all three sister to Koeberliniaceae. First realized to be undescribed in 2010, T. karasense is a rare species known only from three localities in the arid Karas Region, southern Namibia. These small shrubs grow near the edges of seasonal pans on calcareous substrate underlaid by shales and mudstones of the Prince Albert Formation of the Karoo Supergroup. Morphological characters diagnostic of the new family include: a marked differentiation into long and short shoots; dimorphic, spirally arranged leaves; glucosinolate production; bisexual laterally flattened flowers borne singly in bract axils on short shoots only; tetramerous calyx, corolla and androecium with fused sepals and free, non-clawed petals; a staminal disc, but no nectary glands; deeply bilobed ovary with a gynobasic style; S-shaped gynophore supporting a bilocular, horizontally orientated or inverted ovary; two ovules per locule; and a dry, persistent fruit, provisionally interpreted as a one-seeded nutlet. Based on IUCN Red List categories and criteria, a conservation assessment of Vulnerable (VU D1) is recommended for Tiganophyton karasense.
Keywords: Bataceae, Brassicales, Koeberliniaceae, limestone, mudstone, seasonal pans, Karoo Supergroup, endemism, Karas Region, Salvadoraceae, taxonomy, Tiganophytaceae, Tiganophyton, Eudicots
Tiganophytaceae Swanepoel, F.Forest & A.E.vanWyk, fam. nov.
Type:–– Tiganophyton Swanepoel, F.Forest & A.E.van Wyk.
A member of Brassicales, our new family is most closely related to Bataceae and Salvadoraceae and more distantly to Koeberliniaceae. It is morphologically distinct from these and all other known families of the order and easily distinguished by, amongst others, the following combination of characters (for a more comprehensive comparison, see Table 1): dwarf shrub with stems distinctly differentiated into long and short shoots; leaves minute, dimorphic, spirally arranged; glucosinolates present; flowers bisexual, laterally flattened, borne singly in bract axils on short shoots only; calyx, corolla and androecium tetramerous; sepals fused; petals free, not clawed; staminal disc (receptacle?) present; nectary glands absent; ovary deeply bilobed, apparently bilocular; gynophore present, bent in near S-shape; ovary horizontally orientated or occasionally inverted; style gynobasic; ovules two per locule; fruit a dry, persistent, oneseeded nutlet.
Tiganophytaceae differ from Bataceae, Salvadoraceae and Koeberliniaceae by the distinct differentiation of vegetative axes into long and short shoots (vs. mainly long shoots), dimorphic foliage leaves (vs. monomorphic), fruit a nutlet (vs. berry or drupe), ovary bilobed and horizontally orientated or inverted (vs. not lobed and upright), and gynobasic style (vs. apical). It furthermore is easily distinguished from Bataceae by spirally arranged leaves (vs. decussate), hermaphroditic plants (vs. monoecious or dioecious), no stipules (vs. present, early deciduous), solitary flowers in bract axils (vs. in cone-like spikes), sessile petals (vs. long clawed in males; absent in females), gynophore present (vs. absent), and two ovules per locule (vs. one); from Salvadoraceae it differs also by having no stipules (vs. present), spirally arranged leaves (vs. opposite), solitary flowers in bract axils (vs. racemes, panicles or axillary fascicles), free petals (vs. basally fused), no nectar glands (vs. often present), and well-developed and near S-shaped gynophore (vs. absent or short and straight); from Koeberliniaceae it differs also by the lack of thorns (vs. present), solitary flowers in bract axils (vs. axillary umbel-like racemes), fused sepals (vs. free), sessile petals (vs. shortly clawed), four stamens (vs. eight, rarely ten), no separate nectar glands (vs. present), and two ovules per locule (vs. many).
As families, Tiganophytaceae, Bataceae and Koeberliniaceae are morphologically distinct. However, our molecular evidence indicates that Bataceae are nested in Salvadoraceae (also Sun et al. 2016), making Salvadoraceae paraphyletic, but data on more taxa are needed to fully resolve the possible relationships among these families. A phylogenetic analysis of Brassicales inferred from 72 plastid genes by Edger et al. (2018) showed Salvadoraceae and Bataceae to be sisters, but this is of little significance for our use as it was based on a limited sampling of Salvadoraceae, with both Dobera and Azima absent. From a practical point of view, it would serve little purpose to create heterogeneous families with little or no predictive value, although some may argue that monotypic families do little in the way of summarizing information, perhaps preferring to opt for subfamily or tribal status. Considering available evidence for these families, indications are that the largest one, Salvadoraceae, is heterogeneous as currently circumscribed. For example, Azima is, amongst others, morphologically and anatomically distinct from other members of the family (e.g. Takhtajan 2009), and in the past has been placed in a family of its own, namely Azimaceae (Wight & Gardner 1845). However, Azima does share some morphological features with Batis, notably the possession of unisexual flowers (Ronse De Craene 2005) and an ovary with a false septum, albeit only an apical one (Kshetrapal 1970), as is also present in Dobera (Ronse De Craene & Wanntop 2009). Further studies should consider, amongst others, the possible reinstatement of Azimaceae, but alternatively it may be better to accommodate Azima in an expanded Bataceae or to subsume Bataceae in an expanded Salvadoraceae.
Tiganophyton Swanepoel, F.Forest & A.E.van Wyk, gen. nov.
Tiganophyton karasense Swanepoel, F.Forest & A.E.van Wyk, sp. nov.
Type:— NAMIBIA. Karas Region: Groot Pan, 38 km northeast of Tses along road, on edge of pan, 2518CB, 1030 m, 19 December 2010, Swanepoel 365 (holotype WIND; isotypes PRE, PRU).
Conservation status:— Tiganophyton karasense is rare and localized with only three locations known. It should be considered as Vulnerable (VU D1) due to its small population size, the latter estimated to number fewer than 1000 mature individuals (IUCN 2012).
Etymology:— Tiganophyton is derived from the Greek τηγάνι, tigani, a frying pan, referring to the habitat of this species, which can be extremely hot, and φυτών, fyton, a plant. The specific epithet “karasense” denotes the Karas Region in southern Namibia, where all known localities of the new species are located.
Wessel Swanepoel, Mark W. Chase, Maarten J.M. Christenhusz, Olivier Maurin, Félix Forest and Abraham E. E. van Wyk. 2020. From the Frying Pan: An Unusual Dwarf Shrub from Namibia Turns Out To Be A New Brassicalean Family. Phytotaxa. 439(3); 171–185. DOI: 10.11646/phytotaxa.439.3.1