Comparative Morphology and Molecular Systematics of African Podostemaceae‐Podostemoideae, with Emphasis on Dicraeanthus and Ledermanniella from Cameroon

Abstract

The Podostemaceae (eudicots, Malpighiales) are adapted to rivers that exhibit distinct high-low water seasonality, mainly in the tropics. They attach to submerged rocks with ribbonlike or crustose green roots that cover the substrate like a carpet. Pronounced root dorsiventrality resulted in disklike crusts lacking root caps. African Podostemoideae show a bewildering array of forms not known from other flowering plants, such as (i) foliage leaves having a basis with two sheaths (e.g., Ledermanniella linearifolia), (ii) modular shoot construction with repeated stem cups (Ledermanniella ledermannii), (iii) endogenous origin of flowers along stems (Dicraeanthus africanus), and (iv) epiphyllous flowers (Ledermanniella letouzeyi). Important morphological transformations specific to African podostemoids include a shift from erect to inverted flowers in the spathella and unilocular ovaries arising via septum loss. New matK sequence data and new morphological data for eight African Podostemaceae species of the genera Dicraeanthus, Djinga, and Ledermanniella are combined with previously published sequences representing all major groups to test the placement of the African taxa in the family. All podostemoids studied from continental Africa form a clade that is sister to the Madagascan genera Endocaulos and Thelethylax. The sister of this African-Madagascan lineage is the clade comprising all Asian podostemoids and the American genus Podostemum, whereas all other New World podostemoids and the subfamily Tristichoideae are more basal.

A synoptic revision of Inversodicraea (Podostemaceae)

“…Branching of the root-thallus occurs endogenously (arising from the interior, not budding off from the exterior) where it has been recorded (Moline et al (2007) and Thiv et al (2009)). This has been confirmed in I. achoundongii (Schenk et al 2015: 542), and we have observed this also, e.g., in I. feika (Fig.…”

“…bosii, and I. cristata, have been presented in detail by Moline et al (2007) and Thiv et al (2009). This information was part of their wider study of about ten species of African Podostemoideae.…”

“…Here we give an overview of the different structures found in the genus Inversodicraea, and their range in variation across the 30 currently known species of the genus. The overview is based on morphological observations made when researching this paper, combined with data from Cusset (1983) and the excellent in-depth studies of the three species reported by Moline et al (2007) and Thiv et al (2009).…”

“…A single dorsiventrally flattened vascular bundle is present. A rootcap is lacking (Moline et al (2007) and Thiv et al (2009)). Disc-like hold fasts are produced where leaves arise from the margin of the root (I. ledermannii: Moline et al 2007: f. 2C).…”

“…Stems subtended by leaves, arise from both margins of the root, either alternating (I. ledermannii, Moline et al 2007: f. 2C) or opposite to each other as in I. feika ( Fig. 2) and I. achoundongii (Schenk et al 2015), but for most species these data are either not preserved or not recorded.…”