Olax thouarsii (DC.) Valeton

Rogers, Zachary S., Malécot, Valéry & Sikes, Kendra G., 2006, A synoptic revision of Olax L. (Olacaceae) in Madagascar and the Comoro Islands, Adansonia (3) 28 (1), pp. 71-100: 93-96

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Olax thouarsii (DC.) Valeton


8. Olax thouarsii (DC.) Valeton  

( Fig. 8 View FIG )

Critisch Overzicht der Olacineae B. et H. 120 (1886). — Pseudaleioides thouarsii DC.   , Prodromus   1: 533 (1824). — Type: Madagascar, without precise locality, fl., Du Petit-Thouars s. n. (holo-, P-00148726!; iso-, B-W 865!).

Olax pseudaleioides Willd. ex Steud.   , as “ pseudoleioides ”, Nomenclator Botanicus 1: 562 (1821), nom. nud.

Pseudaleia thouarsii Willd. ex Steud., Nomenclator Botanicus   , ed. 2, 2: 208 (1841), nom. inval. pro syn.

Olax glabriflora Danguy   , Bulletin du Muséum d’Histoire naturelle (Paris) 28: 248 (1922). — Type: Madagascar, Prov. Toamasina, Forêt d’Analamazaotra, [18°56’S, 48°26’E], [1000 m], 8.XII.1908, fl., Thouvenot 32 [= Gouvernement de Madagascar 32] (lecto-, P-0048885!, here designated; iso-, P[2]!); syn. nov.

ADDITIONAL MATERIAL EXAMINED. — Madagascar. Prov. Antsiranana, Fivondronana Ambanja, Commune Ambodimanga Ramena, Fokontany Antsahabe , Tsaratanana RNI, 500 m N of junction of Andilambe and Ramena rivers, 13°51’41”S, 48°50’58”E, 536 m, 13.XI.2001, imm. fr., Antilahimena & Birkinshaw 792 (G!, K!, MO!, P, TAN, WAG!) GoogleMaps   . — Marojejy RNI, Sambava , 14°26’10”S, 49°44’25”E, 1200 m, 29-31.III.1995, fr., Rasoavimbahoaka 583 (MO, P, TAN!) GoogleMaps   . — Antsirabe-Nord, environs Sud d’Antsirabe-Nord, route Vohémar-Sambava , [14°00’S, 49°58’E], 18.X.1966, fl., SF (Capuron) 24902 (P[3]!, TEF!) GoogleMaps   .

Prov. Fiananarantsoa, Ambohimanga Sud, Ankatsaoka, Analavory, [20°52’30”S, 47°35’30”E], 15.XI.1963, ster., SF 17-R-497 (P!).

Prov. Toamasina, Ambatovy, Phelps Dodge project site, c. 15 air-km NE of Moramanga, c. 11 km E of Antanambao, 18°52’06”S, 48°18’23”E, 975 m, 15.II.1997, ster., Andriatsiferana et al. 2138 ( MO!) GoogleMaps   . — Same locality, 18°49’48”S, 48°18’54”E, 1175 m, 28.II.1997, fr., Rakotomalaza et al. 1199 (P!). — Same locality, 18°48’28”E, 48°20’03”E, 1100 m, 1.II.2006, ster., Rogers et al. 1001 ( MO!) GoogleMaps   . — Andranobe, Masoala Peninsula, S of Ambanizana, 15°41’S, 49°58’E, 200-400 m, 20.II.1999, fr., McPherson et al. 17635 (MO!, TAN) GoogleMaps   . — Analamazaotra RS, Périnet-Moramanga, [18°56’S, 48°26’E], [1000 m], 22.I.1948, fl., RN (Ratovoarison) 1319 (P!). — Same locality, 19.III.1951, fr., SF ( Zafindraboto ) 3325 (P!, TEF!) GoogleMaps   . — Same locality and date, fr., SF 3735 (P!, TEF!)   . — Sahajinja, bassin de la Manonga (affluent rive gauche de la Rantabe), [15°38’S, 49°25’E], 850 m, 4.III.1954, fr., SF ( Capuron ) 9100 (P!, TEF!) GoogleMaps   . — Périnet-Analamazaotra RS, Périnet, Moramanga, [18°56’S, 48°26’E], [1000 m], 29.IV.1955, fr., SF ( Bégué ) 13387 (P!, TEF!) GoogleMaps   . — Mananara Avaratra PN, Sud de Mananara, [16°26’S, 49°50’30”E], 10.XI.1964, fl., SF ( Capuron ) 23754 (MO!, P[3]!, TEF!) GoogleMaps   . — Tampolo STF, au Nord de Fénérive, [17°17’S, 49°23’E], 9.III.1965, imm. fr., SF ( Capuron ) 24046 (P!, TAN, TEF!) GoogleMaps   . — Tampolo STF, Fénérive Est, 17°17’S, 49°23’E, I.1986, fl., SF ( Rabevohitra ) 32775 ( TEF!) GoogleMaps   . — Analamazaotra, [18°56’S, 48°26’E], [1000 m], I.1919, fl., Thouvenot 76 (K!, P[2]!) [syntype of O. glabriflora   ] GoogleMaps   .


Olax thouarsii   has flowers with 5 or 6 (rarely 4) petals, 6 (rarely 5 or 7) stamens, 3-5 (rarely 0-2) staminodes, and an accrescent calyx (c. 7-11 mm in diam.) that surrounds only the base of the fruit and remains chartaceous. Olax thouarsii   differs from O. antsiranensis   , a species of close affinity, by its longer leaves (5-12 vs. 1.5-4 cm long), ovate or elliptic leaves and foliose bracts (vs. elliptic, ovate-elliptic or rarely obovate leaves and bracts), and by the larger (0.6-1 vs. 0-0.3 mm long), more pubescent, petal ligule. Some care should be taken when measuring leafy organs so as not to confuse true leaves with foliose bracts (see next paragraph).


Morphology of leaf, bract, and inflorescence is strongly influenced by rainfall in the drier months (i.e. March to September). Plants in more humid areas (e.g., coastal and subcoastal populations around Tamatave and Masoala, where 100 mm of rain falls in the driest months) have large persistent leaves and normal racemose inflorescences with short internodes and small membranous bracts. However, on the central plateau (e.g., Andasibe-Périnet, Marojejy, where in the driest months less than 10 mm rain per month is received) true leaves are deciduous to prevent water loss through transpiration. Thus, flowering occurs in the absence of photosynthetically active leaves when the dry season is over (i.e. October through January), inflorescence bracts become leafy, and internodes along the axis elongate. During these times, true leaves remain absent from the infructescence as well. Most collections made from inland populations consist, in their entirety, of large, many-flowered, pseudosolitary inflorescences and no true leaves are present. These collections were previously considered to represent Olax glabriflora   by Danguy (1922), Cavaco & Keraudren (1955a) and Capuron (1968). Foliose bracts in these specimens can reach 3.5 × 1.4 cm in size and resemble true leaves with respect to shape, venation, and often texture. Some true leaves can persist during the deciduous phase in portions of the plant where little or no flowering occurs, but these sterile branches are rarely collected for herbarium specimens.

We were first able to detect the effect of climate on morphology of the species by examining the P sheet of SF 24902, which possesses a large pseudosolitary inflorescence of consistently foliose bracts and a much smaller branch of true leaves intermixed with a few small pseudosolitary inflorescences. Surprisingly, Capuron failed to mention the presence of larger leaves in his discussion of the species, despite making the collection himself and using one of the branches in his illustration of Olax glabriflora   ( Capuron 1968: pl. 1, no. 1). A similar, albeit less dramatic, effect of climate on leaf and inflorescence morphology occurs on some specimens of O. antsiranensis   , a putative Malagasy relative, and the African O. subscorpioidea Oliv.  

The genus Pseudaleioides (Du Petit-Thouars 1806)   was based on type material collected by Du Petit-Thouars, and first published validly without reference to a species name. Steudel (1821) invalidly published Olax pseudaleioides   , as he had O. pseudaleia   (see discussion under O. madagascariensis   ). De Candolle (1824) validated a specific epithet in the genus with the description of Pseudaleioides thouarsii   , citing Du Petit-Thouars’ original description, nearly word-forword, and thereby indirectly referring to the same type material (application of Art.7.7, and for a similar example see Art. 41.3, Ex. 3 in Greuter et al. 2000).

In the Flore, Cavaco & Keraudren (1955a) incorrectly attributed the authorship of the species’ combinational name to Baillon, having overlooked Valeton’s (1886) earlier valid combination in Olax   . Baillon (1862) never made the combination, instead he cited Olax pseudaleioides   as a correct name with Pseudaleioides thouarsii   listed as a synonym.


Olax thouarsii   occurs at several mid-elevation sites along the eastern escarpment of the central plateau, with a few populations growing at lower elevation near the east coast (Fig. 11). The estimated elevational range for the species is 0 to 1200 m. Olax thouarsii   flowers October through January and fruits from November through April.


Maitsohely (SF 9100); Maitsoririnina (Andriatsiferana et al. 2138; RN 1319; SF 3325, 3735, 13387, 32775); Manarombita (SF 17-R-497).


Olax thouarsii   has been recorded in several of Madagascar’s protected areas (Analamazaotra, Marojejy, Masoala,Tampolo,Tsaratanana, and possibly Mananara Avaratra).The EOO is 78 000 km 2, whereas the AOO is 80 000 km2 (grid cell size 100 × 100 km). The species is assigned a provisional conservation status of Least Concern (LC).


In the Flore, Cavaco & Keraudren (1955a) cited the type of Pseudaleioides thouarsii   as “ Madagascar, sans indication: du Petit-Thouars 533 (type)”. However, “533” is not a collection number; it is the page number where the name appears in the protologue ( De Candolle 1824). One flowering specimen at P (P-00148726) bears a typewritten “Du Petit- Thouars” label and matches the original description. Two anonymous annotations, “ O. thouarsii   ” and “ O. pseudaleioides Steud.   ”, are inscribed on the sheet. The latter of the two was presumably written by Capuron, who chose to recognize Steudel’s name as valid in his 1968 report.

Two sheets filed under Pseudaleia   (B-W 866) and Pseudaleioides   (B-W 865)in the Willdenow herbarium are mislabelled.Sheet B-W865 taxonomically belongs to Pseudaleioides thouarsii DC.   (= Olax thouarsii (DC.) Valeton   ) but was annotated as “ Ol. Pseudaleja ”, while B-W 866 was incorrectly identified as Pseudaleia madagascariensis DC.   (= Olax madagascariensis (DC.) Valeton   , species no. 6) and annotated as “ Ol. Pseudalejoides ”. Sheet P-00148726 should be regarded as the holotype of Pseudaleioides thouarsii   and sheet B-W 865 probably represents an isotype.

Two collections (Thouvenot 32, 76) were cited in the protologue of Olax glabriflora   . Both closely match the description in the protologue ( Danguy 1922). Thouvenot 32 is in the best physical condition and three sheets of this particular syntype are deposited at P. One of these, P-00048885, bears some detailed notes on floral morphology and includes an illustration of a dissected flower, making it the most suitable choice for lectotype.



Parc de Tsimbazaza


Wageningen University


Centre National de la Recherche Appliquée au Developement Rural


Missouri Botanical Garden














Olax thouarsii (DC.) Valeton

Rogers, Zachary S., Malécot, Valéry & Sikes, Kendra G. 2006

Olax pseudaleioides Willd. ex

Steud. 1821: 562