Apodocephala

Bengtson, Annika & Razafimandimbison, Sylvain G., 2024, New subtribal and generic limits in the tribe Athroismeae (Asteraceae) and further disintegration of the subtribe Madagasterinae of the tribe Astereae, Willdenowia 54 (1), pp. 103-116 : 109-111

Phylogenetic relationships within Apodocephala

Apodocephala currently consists of nine species of trees or shrubs with discoid paleate capitula in terminal corymbiform-paniculate inflorescences, all endemic to Madagascar: A. angustifolia , A. begueana , A. coursii , A. minor , A. multiflora , A. oliganthoides , A. pauciflora , A. radula and A. urschiana . Our analyses demonstrate that Apodocephala is paraphyletic with respect to the monospecific Malagasy genus Lowryanthus (here represented by two individuals of L. rubens ). This is inconsistent with Bengtson & al. (2021), who resolved Lowryanthus as sister to two species of Apodocephala ( Fig. 3 ). Apodocephala is resolved into two major clades: one containing A. minor , A. radula and L. rubens and the other formed by A. angustifolia , A. begueana , A. multiflora , A. oliganthoides , A. pauciflora and A. urschiana . Apodocephala and Lowryanthus mainly differ in the colour of the peduncles, capitula and florets ( Fig. 1A, B ). The latter has a striking appearance with bright red inflorescences and florets, whereas Apodocephala has florets with white or whitish corollas. Aside from that, L. rubens resembles Apodocephala , both consist of shrubs or trees with discoid mainly few-flowered paleate capitula in terminal corymbiform-paniculate inflorescences and have cypselas that lack a true pappus. Bengtson & al. (2021) noted additional similarities in the cypselas of Lowryanthus and Apodocephala ( Fig. 4 ). Lowryanthus has geniculaterostrate cypselas with a tightly curved rostrum ( Pruski 2014), a character also found in several species of Apodocephala . The flattened rostrate cypselas of A. coursii and A. radula (see Humbert 1962: 86) especially resemble those of L. rubens , but A. minor and A. urschiana also have cypselas with a narrowed curved rostrum ( Fig. 4 ; Humbert 1960, 1962). The character therefore occurs in both clades ( Fig. 3 , 4 ).

The two major clades of Apodocephala are geographically separated. Apodocephala minor and A. radula are both found in close geographical proximity of the known localities of Lowryanthus rubens in southeastern Madagascar. However, the three species do not grow sympatrically and occupy different habitats. Lowryanthus rubens is found in low-elevation humid evergreen forests from 100–300 m in elevation, whereas A. radula is found in siliceous rocky habitats at higher elevations and A. minor grows in rocky habitats at low elevations ( Humbert 1960; Pruski 2014). The remaining sampled Apodocephala species form a well-supported clade ( Fig. 3 ) and have a much wider geographic distribution along eastern Madagascar, ranging from Ivohibe in the southeast to Daraina in northern Madagascar. It can be concluded that geographic proximity is sometimes a better predictor of evolutionary history than morphology; a similar pattern has recently been reported from the Malagasy endemic Rubiaceae genera Payera Baill. and Schismatoclada Baker ( Razafimandimbison & al. 2022). Despite the geographical separation of the two clades, we argue that Lowryanthus should be formally merged in Apodocephala (which has the priority over the former), because there is no morphological difference between the two clades that would justify dividing Apodocephala in two.

Humbert (1955) divided Apodocephala pauciflora into two varieties, A. pauciflora var. pauciflora and A. pauciflora var. cacuminum , differing in leaf size and shape (see Table 1 ) as well as in shape of involucral bracts and capitulum size, where A. pauciflora var. cacuminum appears to have somewhat larger capitula. Morphological comparisons also show differences in the shape of the cypselas, which are shorter and more subprismatic in var. cacuminum ( Fig. 4G, H ). The two varieties differ in distribution and habitat. Apodocephala pauciflora var. pauciflora grows in rainforests at 800–1900 m in elevation and has a wider distribution ranging from Marojejy in the northeast to Fianarantsoa in central Madagascar. In contrast, A. pauciflora var. cacuminum is restricted to the Marojejy massif in the northeast, where it is found in ericoid vegetation in rocky places from 1300 to over 2000 m in elevation ( Humbert 1955, 1960). Further, A. pauciflora var. pauciflora and var. cacuminum also appear to differ in flowering time ( Table 1 ). Analyses place the two varieties in different clades, a specimen of A. pauciflora var. pauciflora is placed sister to A. begueana , in a clade also consisting of A. urschiana and A. angustifolia , whereas two specimens of A. pauciflora var. cacuminum form a monophyletic group sister to A. oliganthoides in a clade comprising also A. multiflora ( Fig. 3 ). Apodocephala pauciflora var. cacuminum resembles A. oliganthoides in having oblanceolate leaves and capitula with rounded involucral bracts. Our results support that A. pauciflora var. pauciflora and var. cacuminum should be considered separate species.

Apodocephala coursii could not be included in the molecular study, but morphological comparison shows similarities to A. radula and A. rubens , and it is likely to be closely related to those species. Apodocephala coursii , A. radula and A. rubens all have similar flattened cypselas with a curved rostrum, and A. coursii and A. rubens also have cypselas with long marginal and apical trichomes ( Humbert 1960, 1962; Pruski 2014). Apodocephala coursii , A. radula and A. rubens all have distributions in southeastern Madagascar. Apodocephala coursii is only known from the Atsimo-Atsinanana region in eastern Madagascar where it grows in rainforest vegetation ( Humbert 1962).

Based on the evidence presented above, two new combinations are made: Apodocephala rubens (Pruski) Bengtson & Razafim. and A. cacuminum (Humbert) Bengtson & Razafim. (see below).

Figures

Fig. 3. Bayesian fifty-percent majority-rule consensus tree from an analysis of the combined Athroismeae dataset (including ETS, ITS, ndhF and trnL-trnF). Numbers above branches indicate posterior probability (PP) and bootstrap values (BS), bootstrap values <50 are indicated by a dash. Scale bar shows number of substitutions per site.

Fig. 1. A: Apodocephala pauciflora; B: Lowryanthus rubens; C: Jalantzia (Vernoniopsis) caudata; D: Rochonia cinerarioides; E: Madagaster sp. – Photographs by S. E. Rakotoarisoa (A; CC BY-NC © 2023), M. Thulin (B; CC BY-NC-SA © 2023), S. Razafimandimbison (C, E) and M. Arnerup (D).

Fig. 4. Cypselas – A, B: Lowryanthus rubens, Razafimandimbison & al. 1531 (S); C, D: Apodocephala radula, Humbert 20708 (S); E: A. minor, Sabouraeu (P); F: A. urschiana, McPherson & van den Werff 16551 (MO); G: A. pauciflora var. pauciflora, Turk & Randriamanatena 203 (MO); H: A. pauciflora var. cacuminum, Razafimandimbison & Razafindrahaja 2951 (S); I: A. oliganthoides, Razafimandimbison & Razafindrahaja 2975 (S); J: A. multiflora, Ranarivelo & Ravelnarivo 771 (MO); K: A. begueana, Service Forestier de Madagascar 13551-SF (P); L: A. angustifolia, Rakotomalala & Narison 124 (MO). – All scale bars = 1 mm.