Phylogenetic positions of Vernoniopsis and Rochonia

Nesom (2020) placed the Malagasy genera Apodocephala, Vernoniopsis, Rochonia and Madagaster in his new subtribe, Madagasterinae of the tribe Astereae, based on their arborescent habit with coriaceous abaxially tomentose leaves, caudate anther thecae and isolated geographic distribution. Madagaster has been confirmed to be a member of the tribe Astereae (Brouillet & al. 2009); however, Apodocephala was recently shown to belong to the tribe Athroismeae and transferred there (Bengtson & al. 2021), implying the non-monophyly of Madagasterinae as defined by Nesom (2020). The monophyly of Madagasterinae is further rejected by our analyses, because Vernoniopsis was resolved sister to the Apodocephala - Lowryanthus clade (Fig. 2, 3). Vernoniopsis is therefore another addition to the Athroismeae (Fig. 2, 3).

The phylogenetic position of Rochonia (here represented by R. cinerarioides) within Astereae is strongly supported (Fig. 2), consistent with Nesom (2020). Rochonia consists of four species of shrubs or subshrubs with radiate capitula bearing ray florets with yellow corollas (Fig. 1D). The genus resembles Madagaster in morphology, and Humbert (1932) even described the taxa currently placed under Madagaster and Rochonia (then Aster L.) as mainly differing in the colour of the ray floret corollas (Madagaster have ray florets with white to bluish corollas). Nesom (1993) described the genus Madagaster for the white-rayed species, considered to be a lineage separate from, but close to, Rochonia. We agree that Madagaster and Rochonia are likely to be closely related based on their morphological similarities; however, whether they are sisters remains to be seen. In summary, only two out of the four genera of Nesom’s (2020) subtribe Madagasterinae, Madagaster and Rochonia, remain.

Monophyly of Vernoniopsis (now Jalantzia)

Our analyses strongly support the monophyly of Vernoniopsis (here represented by its two species, V. caudata (Drake) Humbert and V. lokohensis (Humbert) Callm. & Phillipson; Callmander & Phillipson 2011) and its phylogenetic position in the tribe Athroismeae as delimited by Bengtson & al. (2021), where it is resolved as sister to the Apodocephala - Lowryanthus clade (Fig. 2, 3). This finding is inconsistent with Bremer (1994) and Nesom (2020), who classified the genus in the tribe Astereae. Members of Vernoniopsis are shrubs or small trees with coriaceous leaves and discoid homogamous capitula containing 1–4 florets with white corollas (Fig. 1C; Humbert 1960; Callmander & Phillipson 2011). Vernoniopsis caudata, the generitype, was originally described by Drake (1899) as Vernonia caudata Drake because of its Vernonia -like habit and inflorescences, inconsistent with our results. Humbert (1955) totally rejected this taxonomic decision and described his new genus Vernoniopsis to accommodate Vernonia caudata in the tribe Astereae based on differences in the stigmatic surfaces of the style branches. The name Vernoniopsis was recently noted to be an illegitimate later homonym of Vernoniopsis Dusén and has therefore been replaced by Jalantzia D. J. N. Hind (Hind & Langhorne 2024). The recognition of Vernoniopsis (now Jalantzia) at generic level is consistent with our findings. Jalantzia (Vernoniopsis) has been suggested to be closely related to the Malagasy genus Apodocephala based on their discoid capitula with white corollas and the presence of shortly caudate anthers (Humbert 1960; Bremer 1994; Nesom 2020). The molecular phylogenetic analyses here confirm the close relationship of Apodocephala and Jalantzia (Fig. 2, 3). Jalantzia differs from Apodocephala in having epaleate receptacles and a pappus of scabrid bristles, whereas Apodocephala has paleate receptacles and lacks a true pappus. Therefore, we maintain the current generic status of Jalantzia.

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Further, our analyses support the recognition of Vernoniopsis caudata subsp. lokohensis Humbert at species level (Callmander & Phillipson 2011). Jalantzia (Vernoniopsis) caudata (Drake) D. J. N. Hind and J. lokohensis (Humbert) D. J. N. Hind do not grow sympatrically. The former commonly grows along the littoral forests of the eastern coast of Madagascar, while the latter is restricted to the highland rainforests of the Marojejy massif in northeastern Madagascar between 1300 and 2000 m in elevation. In other words, Jalantzia (Vernoniopsis) contains two geographically distinct lineages, the northeastern group (J. lokohensis) and the eastern-southeastern group (J. caudata). A similar pattern has recently been reported by Razafimandimbison & al. (2022) in the Malagasy Schismatoclada farahimpensis Homolle (Rubiaceae), which was resolved in two geographically and morphologically distinct lineages: northern and southern groups, that could be recognized at subspecies level (Razafimandimbison, unpublished data).