Sapindus marikuru A. R. Franck, sp. nov.
Creators: name: Franck, Alan R.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Sapindales
Sapindaceae
Sapindus
Sapindus marikuru

description: 4. Sapindus marikuru A.R. Franck, sp. nov. (LSID: 77340321-1) (Figure 9).
Type:— RAPA NUI (Easter Island, Chile). Rano Kao Crater, 17 January 1935, J.P. Chapin 1026 (holotype: NY03227768!; isotypes: A01771330!, BISH179846!).
Diagnosis:— Sapindus marikuru is most similar to S. saponaria. The distinctive characters of S. marikuru are the petiolules (0) 3–11 mm long and glabrate leaflets 3.1–5.5 times longer than wide with orangish venation and strongly prominent reticulate venation (vs. petiolules 0–5 mm long and glabrous to moderately pubescent leaflets 1.6–3.5[5] times longer than wide with pale green to pale yellow venation and prominulous to obscure reticulate venation in S. saponaria). Sapindus thurstonii (endemic to Hawaii) differs by its pubescent and dark leaflets, petiolules 0–3 mm long, and its brown-speckled petiole base (vs. glabrate, green leaflets with petiolules usually 3–11 mm long and the petiole base yellowish in S. marikuru). Sapindus marikuru is placed in the identification key assuming it has larger fruits like S. saponaria. Sapindus marikuru can be distinguished from the other species of Sapindus with small fruits by its leaflet blades 3.1–5.5 times longer than wide with prominent reticulate venation and petiolules (0) 3–11 mm long (vs. leaflet blades 2.5–3.5 times longer than wide with prominent reticulate venation and petiolules 1–4 mm long in S. balicus, leaflet blades 1.5–2.5 times longer than wide with prominulous to obscure reticulate venation and petiolules 0–1 mm long in S. motu-koita, and leaflet blades 2.5–5.5 times longer than wide with prominent to nearly obscure reticulate venation and petiolules 0–1 mm long in S. tricarpus).
Etymology:—For marikuru, the local name of the species on Rapa Nui (Guillaumin et al. 1936).
Description:—Tree, to 8 m. Petiole 1.9–6.7 cm long, pale yellow to brown-yellow, unwinged to rarely slightly winged, glabrous to sparsely puberulent; rachis glabrous to sparsely puberulent, usually unwinged, rarely wings on one side of rachis to 3.5 mm wide; leaflets (4)6–8(10); petiolule (0) 3–11 mm long, glabrous to sparsely puberulent; leaflet blade lanceolate, strongly to lightly asymmetric, falcate to slightly falcate, the apex acuminate with an obtuse to bluntly acute tip, 3.5–9.5(12) cm long, 1.3–2.4 cm wide, 3.1–5.5 times longer than wide, adaxially drying dark green to mildly dark green, glabrous or sparsely pubescent along the midrib, the midrib pale brown, brown-orange, to reddish green, at mid-blade the ridge 0.1–0.2 mm wide, 0.1–0.2 mm high, the blade not sunken along the midrib, secondary veins pale brown to brown-orange, tertiary and quaternary (sometimes quinternary) venation strongly raised, prominent and conspicuous, concolorous with the secondary veins and strongly discolorous with the blade surface, abaxially drying pale green, glabrous, midrib pale yellow to orangish yellow, secondary veins pale yellow to slightly orangish, tertiary venation raised and prominent and concolorous with the secondary veins or nearly so, quaternary and quinternary venation somewhat prominent to obscure and nearly concolorous with the blade surface; foveolae inconspicuous, exudate clear. Petals not observed. Fruit not observed.
Distribution, habitat, and phenology:—Rapa Nui (Easter Island, Chile) (Fig. 3), 100– 150 m. Open, disturbed areas. Flowering January–February(?).
Notes:—The plants of Rapa Nui, S. marikuru, are distinctive for their long petioles, long petiolules, and glabrate, narrow, falcate leaflets with orangish venation and strongly prominent reticulate venation. It is presumed that the ovaries and fruit are glabrous and the petals lack appendages, similar to the other species of Oceania and South America, but mature flowers and fruits have not been observed. Its fairly narrowly lanceolate, falcate leaflets drying green seem most like S. saponaria subsp. saponaria from continental America (Seeman 1865), such as Soukup 4232 from Peru which displays somewhat orangish venation on the leaflets like S. marikuru.
Rapa Nui harbors ca. 65 native plant species (Zizka 1991, Zizka & Zizka 2022). Few extant plant species are endemic to Rapa Nui, previously including only four angiosperms and three mosses (Zizka 1991, Zizka & Zizka 2022). The plants of Sapindus on Easter Island had always been assumed to belong to S. saponaria, and opinions varied on whether it was native or a recent anthropogenic introduction (Fuentes 1913, Skottsberg 1928, Langdon 1996, Zizka 1991, Dubois et al. 2013, Rull 2021, 2022, Zizka & Zizka 2022). The unique morphology of S. marikuru supports its recognition as an endemic species, existing long before human habitation. Pollen of Sapindus was putatively present 28–12,000 years ago on Easter Island (Flenley et al. 1991, Butler & Flenley 2010, Gossen 2011) and existed before and after European visitation (Orliac 2000, Rull 2021, Zizka & Zizka 2022). At times, it had been assumed that all populations of Sapindus in the eastern Pacific Islands were the same taxon (Langdon 1996), but Sapindus marikuru is unlike S. saponaria subsp. jardinianus from French Polynesia and the Cook Islands, and distinct from S. saponaria subsp. saponaria in the Americas.
The species was probably noted by Cook’s (1777: 285, Forster 1786: 29) party on 15 March 1774, “At the S.W. corner of the island, they found another small shrub, whose wood was white and brittle, and in some measure, as also its leaf, resembling the ash.” In the same month (and perhaps the same day), J.R. Forster & G. Forster made a collection of the species, now at the BM herbarium. The Forster specimen is unlike all other specimens observed in having nearly sessile leaflets and a winged rachis. Probably, the Forster specimen is from an immature plant or sprout, as elsewhere in the genus such leaves tend to be more strongly winged than on mature stems. The wood of S. marikuru was recorded as being used on Easter Island (Métraux 1940), specifically for a white pigment (McCoy 1978) or wood carving according to Chapin 1026.
Conservation Status:— Zizka (1991) stated that there are only a few old plants and no fruiting plants were known. Alvarez & Sperling (2010) reported that the species only existed as “small stump suckers” in the wild and Dubois et al. (2013) reported less than 10 individuals in the wild. Some efforts to propagate Sapindus took place on the island (Alvarez & Sperling 2010; Rull 2022), some using cuttings presumably from native stock (Tassin 2005), and, also using a non-native Sapindus from Hawaii (J.-F. Butaud, pers. comm.; Dubois et al. 2013). The indigenous species of Sapindus on Rapa Nui (S. marikuru) is clearly distinct from the species native to Hawaii (S. saponaria subsp. jardinianus, S. thurstonii, or S. oahuensis) or cultivated in Hawaii (S. saponaria subsp. saponaria). The species S. marikuru should be classified as Critically Endangered (IUCN 2012) and conservation efforts should immediately be focused on S. marikuru to propagate indigenous populations. Any material of Sapindus from Hawaii or elsewhere should be treated as non-native to Rapa Nui.
Specimens examined:—RAPA NUI (EASTER ISLAND, Chile). March 1774, “Specimen 1”, Forster & Forster s.n. (BM); Malikuli, [1920], Bryan s.n. (BISH, RSA); Roiho, Mati-Kuna, 22 October 1934, Drapkin s.n. (SGO); Roiho, südlich Ahu Akivi, 30 April 1988, Zizka 427 (FR); Rano Kao, unterhalb Orongo, 15 January 1991, Zizka 1358 (FR).
description: Published as part of Franck, Alan R., 2024, Revision of Sapindus sect. Sapindus (Sapindeae, Sapindoideae, Sapindaceae), including the description of three new species, pp. 1-71 in Phytotaxa 648 (1) on pages 26-28, DOI: 10.11646/phytotaxa.648.1.1, http://zenodo.org/record/13215835