A revision of Homalium sect. Rhodonisa (Salicaceae) endemic to Madagascar

Abstract Applequist, W.L. (2020). A revision of Homalium sect. Rhodonisa (Salicaceae) endemic to Madagascar. Candollea 75: 245–268. In English, English & French abstracts. Homalium sect. Rhodonisa (Tul.) Sleumer is endemic to Madagascar and has included three recognized species. A new revisionary treatment of the section is presented and an identification key is provided. Twelve species are recognized, of which seven are newly described: Homalium analavelonae Appleq., Homalium ihosyense Appleq., Homalium megaphyllum Appleq., Homalium phillipsonii Appleq., Homalium pseudoracemosum Appleq., Homalium rakotovaoi Appleq., and Homalium vohitsiandrianense Appleq. Two lectotypes are designated. Taxonomic novelties are provided with line drawings or scans of their holotypes. Risk of extinction assessments indicate that two taxa are “Critically Endangered”, one is “Endangered” and four “Vulnerable”. Occasional hybridization is observed. Some specimens are not classifiable and it is possible that other unrecognized species exist.


Introduction
Homalium Jacq. (Salicaceae) is a pantropical woody genus, historically included within the polyphyletic family Flacourtiaceae (Chase et al., 2002). The genus is distinguished by two perianth whorls, a large gland on the adaxial base of each sepal, a semi-inferior ovary and oppositipetalous stamens arranged either singularly or in fascicles. In a recent revision ten sections were recognized, correcting the synonymization of sect. Polyanthera Warb. with sect. Eumyriantheia Warb. by Sleumer (1973), and the two subgenera formerly recognized were not upheld, as the distinguishing feature of a solitary stamen per petal (subg. Blackwellia (Benth.) Warb.) vs. fasciculate stamens (subg. Homalium) appears to be homoplasious (Applequist, 2016a). Before recent re-evaluation of the Malagasy species, about 150 species had been recognized within the genus (Applequist, 2013).
Madagascar and Malesia are the two primary centers of diversity for Homalium. The greatest sectional diversity is ascribed to Madagascar, with six sections, five of which are considered endemic following the restriction of sect. Eumyriantheia to only Malagasy species (Applequist, 2016a). The Malagasy species were revised by Sleumer (1973), who recognized a total of 28 species in Madagascar. However, that treatment had become obsolete due to the great increase in available herbarium material during the intervening 45 years. Recent revisionary studies have described multiple new species in every section treated (Applequist, 2016b(Applequist, , 2018a(Applequist, , 2018bWassel & Applequist, 2020), including sects. Eumyriantheia, Blackwellia Benth., Odontolobus Warb., and Nisa (Noronha ex Thouars) Baill. ex Warb. The endemic sect. Antinisa (Tul.) Baill. ex Warb. contains one species, H. involucratum (DC.) O. Hoffm., within which three geographic variants are recognized as forms (Sleumer, 1973) that probably merit recognition at a higher level.
The final section in need of substantial revision is the Malagasy endemic Homalium sect. Rhodonisa (Tul.) Sleumer, which is treated herein. This section is distinguished by solitary stamens, petals usually accrescent and larger than the sepals (in contrast to sect. Nisa, where the opposite is true), and persistent bracts and bracteoles (Applequist, 2016a). The last taxonomic revision of sect. Rhodonisa (Sleumer, 1973) reported it to include three species. However, H. albiflorum (Boivin ex Tul.) O. Hoffm. was circumscribed to include four species-level taxonomic synonyms and a suspiciously broad range of ecological diversity, so, as for H. nudiflorum (DC.) Baill. in sect. Nisa (Wassel & Applequist, 2020), it appeared evident that this species was much too broadly defined.

Materials and Methods
Materials examined included herbarium specimens at MO, duplicates of MO collections not yet distributed, and specimens from P seen during a visit, with a few potential types received on loan. In addition, images of types held by other institutions available through the JSTOR Plants website [https://plants.jstor.org] were observed, and images of some specimens were obtained from G. Standard taxonomic procedures were followed, consistent with the recent revision of other sections of Homalium in Madagascar (Applequist, 2016a(Applequist, , 2018a(Applequist, , 2018bWassel & Applequist, 2020).
Special comment is necessary regarding certain morphological features in this section. Bark characteristics and floral color are reported whenever label data have provided them. For convenience, atypical characters seen in only one species are noted only in the description of that species. Inflorescences are always exclusively lateral, largely borne in axils of leaves, unless otherwise stated. The petal length increases during the process of floral and fruit maturation, sometimes greatly. Although there are significant differences among species in initial and final corolla size, this character should be used to aid in specimen identification only with caution, because the stage of development can be difficult to determine. As in other sections, fruits that might be considered mature are rarely seen, because the entire flower is quickly deciduous as the unit of dispersal. Therefore, no seed characters are known well enough to be useful, and only vegetative and floral characters and those of the fruiting perianth can be used for identification. Specimens marked as fruiting are identified as such by their expanded perianth and sometimes lost anthers; the ovary may not be significantly expanded.
To save space, locality data are not provided for all specimens seen of the most common taxa, and those that are provided are edited for brevity, especially where more complete label data are available from Tropicos (2020). "Fkt." is used throughout as an abbreviation for "fokontany". A distribution map showing representative localities of species in the Homalium albiflorum complex, approximated as necessary, was produced using QGIS 3.10.7 (QGIS Development Team, 2019) and the Madagascar ecoregions shapefile of Vielledent et al. (2016). A complete index of specimens seen is provided as an appendix. Maps of georeferenced specimens that are databased in Tropicos may be viewed within the Catalogue of the Plants of Madagascar (Madagascar Catalogue, 2020), which is continually updated with new determinations and specimens.
A preliminary, unofficial assessment of conservation status using the categories and criteria of IUCN (2012) is provided for each taxon recognized. If the Extent of Occurrence [EOO] and Area of Occupancy [AOO] could affect the assessed status, GeoCAT (Bachman & Moat, 2012) was used to estimate those values. Geographic coordinates were taken from label data or approximated from the Missouri Botanical Garden's gazetteers or coordinates estimated in prior georeferencing efforts (Tropicos, 2020). If coordinates for a specified locality could not be obtained, coordinates for the closest locatable population center mentioned on the label were used, or databased centroid coordinates for some protected areas from ANGAP (now Madagascar National Parks, MNP).
Notes. -Adequate molecular data to elucidate relationships among the very diverse, probably paraphyletic lineages of Homalium do not exist. The relationships of species of sect. Rhodonisa would be of particular interest. The genus as now circumscribed has an apparent division between Homalium sect. Homalium and similar sections (e.g., in Madagascar, Eumyriantheia and Nisa) and sect. Blackwellia Benth. and related sections (primarily Polyanthera). Species that are typical of the former group have relatively few (4 -7) broad sepals and petals; relatively large, broadly elliptical anthers; large sepal glands; and broadly funnelform calyx cups in flower. Sepals and petals are usually different in shape and may differ in size or accrescence. Typical species of sects. Blackwellia and Polyanthera have often more numerous, narrow sepals and petals, which usually are similar in shape; often small broad anthers with subglobose locules (though broadly elliptical anthers are also seen); and often narrowly funnelform to tubular, ridged calyx cups. The upper surface of the ovary is often prominently conical. Sect. Rhodonisa includes species that have relatively few, broad petals and sepals, like sects. Eumyriantheia and Nisa, but often elongated, narrow, ridged calyx cups, and sometimes also small "Blackwellia-like" anthers with subglobose locules. These species are not easily classed as belonging to either group of sections, which is one reason for this author's preference not to recognize subgenera (Applequist, 2016a). Sleumer (1973) recognized two red-flowered species, H. sanguineum (Boivin ex Tul.) Baill. and H. rubriflorum Sleumer, and one white-flowered species, H. albiflorum, within sect. Rhodonisa. Red flowers are rather unusual in Homalium, though not unknown from other sections, and the two red-flowered species are also distinguished from the H. albiflorum complex in having long-branched paniculate inflorescences and flowers borne only 1 or 1 -2 per node and bract (rather than in clusters of 2 or more). The taxonomy of the red-flowered species is not problematic, and no undescribed similar species were identified.
Notes. -As previously circumscribed (Sleumer, 1973), H. albiflorum encompassed a great range of morphological character states and was distributed almost throughout the entire country of Madagascar (Fig. 2). It is herein restricted to populations with usually elliptical to broadly elliptical leaves, well-developed peduncles, partly pubescent rachises, at least sparsely pubescent perianths, and 5(6)-merous flowers (Fig. 1).
Homalium albiflorum continues to encompass a broad range of morphological variation, possibly due in part to hybridization with or introgression from related species. In northern populations it sometimes has narrow leaves, broadly elliptical anthers, sparse pubescence on the abaxial leaf surface, and/ or occasional domatia. The specimens Afzelius s.n. and Noyes et al. 1061 are identified below as suspected hybrids involving H. pseudoracemosum, but it is possible that they represent aberrant individuals of H. albiflorum. A few other northern collections identified as H. albiflorum have unusually narrow leaves. Below, northern collections with pilose indument that appear morphologically consistent with H. phillipsonii or intermediates between that species and H. albiflorum are noted under that species.
The publication of Nisa albiflora (Tulasne, 1857: 72) cited the collection numbers Pervillé 480 and Boivin 2124 (said to come from "in Macroneso adjacenti"). The only known complete specimen has a handwritten label stating that it was collected by Pervillé under the number 480; below that on the same label is the notation "2124. Nossi-bé. Bernier comm. 1846". A preprinted label referring to Boivin's 1847 -1852 voyage was applied in Paris with the handwritten annotation "2124". This appears to be the origin of an incorrect citation by Tulasne of Boivin. Thus, the name was based only on the single sheet of Pervillé 480 at P (the fragmentary material obtained by L clearly not having the status of a second duplicate). The P specimen was designated as lectotype by Perrier de la Bâthie (1940: 925) but the designation was unnecessary as it is properly regarded as a holotype.
Afzelius s.n. and Noyes et al. 1061 have abnormally narrow leaves and are from the western portion of the range, sympatric with the probably closely related H. pseudoracemosum. They are suspected of having hybrid ancestry.
Distribution, ecology and conservation status. -Homalium analavelonae is known only from one collection from the southwestern massif of Analavelona (Fig. 2). Analavelona is a sacred forest and has some level of protection. Because this forest is subhumid, while forests in surrounding areas are dry (and highly degraded or lost), the species is unlikely to occur anywhere else. This means that the species is vulnerable to having its entire population affected by a single event, so a preliminary assessment of its conservation status is "Vulnerable" [VU D2].

Homalium baillonii
Distribution, ecology and conservation status. -Homalium baillonii is endemic to southeastern Madagascar (Fig. 2). It occurs in littoral forest or low-altitude humid forest, on sand. Its habitat includes the protected areas of Mandena, Ste. Luce, and Andohahela. The EOO is estimated as 10,895 km2, and the AOO as 64 km2. However, the large majority of accurately located collections occur in a very small area, and it is not evident that more than ten distinct populations exist. Because the unprotected portions of the habitat are suffering ongoing anthropogenic degradation and loss, a preliminary estimate of the species' conservation status is "Vulnerable" [B1ab(iii)+B2ab(iii)]. The species was collected outside the Anosy region once in 1954 and never again since then, despite repeated botanical collections in remaining low-altitude and coastal forests. If that population were excluded as probably extinct, the EOO would be estimated as 1403 km2 and the AOO as 60 km2.
Notes. -Homalium baillonii, which was lumped by Sleumer (1973) into H. albiflorum, is herein reinstated as a distinct species. It is distinguished by many characters, including its thick-textured leaves often with subentire margins and proportionally long petioles; short-peduncled, glabrous inflorescences; flowers tetramerous and very short-pedicellate or sessile; and glabrous sepals and petals (except for ciliate sepal margins). Additionally, it is native to southeastern Madagascar and has clearly different ecological preferences (Fig. 2). It is much more similar to H. leucophloeum, also herein removed from H. albiflorum, which almost always has sessile flowers and has proportionately narrower and on average somewhat shorter leaves, which usually have shorter petioles than those of H. baillonii and slightly more prominent veins. That species occurs farther north than H. baillonii, and at least usually at higher elevations. 4. Homalium ihosyense Appleq., sp. nov. (Fig. 4). Tree to 8 m tall; twigs dark brown when young, becoming gray, glabrous. Leaves elliptical (to somewhat obovate or broadly elliptical), (4.7 -)6.7 -14 × (3 -)4 -6.3 cm, thick-textured; margin inconspiculously crenulate; base convex to rounded; apex cuspidate to short-acuminate (obtuse, rounded); both surfaces glabrous, drying greenish (the upper surface sometimes mottled) to grayish (dark brown); secondary veins slightly prominent; petiole 13 -30 mm, glabrous. Inflorescences racemose, (3 -)4.5 -11 cm; peduncle virtually absent; rachis moderately pilose to glabrate; flowers 2 -3 per node; pedicels 0.5 -4.5 mm, short-pilose. Flowers 5-merous, white; sepals narrowly oblong, 1.8 -3 mm, sparsely pilose outside, margins ciliate; sepal glands broadly elliptical, c. 0.6 × 0.5 mm; calyx cup sparsely pilose; petals oblanceolate, 3.5 -12 mm, strongly accrescent, sparsely soft-pubescent to sparsely pilose on both surfaces, margins ciliate; filaments 1.3 -1.7 mm; anthers broadly elliptical, 0.3 mm high. Distribution, ecology and conservation status. -Homalium ihosyense is (or was) endemic to the valley of the Menarahaka near Ihosy (Fig. 2); it was reported to occur in mid-elevation dry forest on sand. The single known population has not been recollected for several decades. The large majority of the native vegetation in this area was unprotected and has been lost since the historical collections were made. This species is certainly to be assessed as "Critically Endangered" [CR B1ab(iii)+B2ab(iii)], if indeed it is not "Extinct in the wild".
Distribution, ecology and conservation status. -Homalium leucophloeum is native to southeastern to northern humid forests, at least usually mid-elevation to high-elevation, and forests of the central plateau (Fig. 2). It has been reported on limestone, marble, and rocky substrate. It is known from over 10 historical populations, including several protected areas (Itremo, Ankafobe, Ankaratra-Manjakatompo, Andringitra, possibly Midongy du Sud and Montagne d'Ambre). Its conservation status is therefore assessed as "Least Concern" [LC]. However, it is of concern that recent collections are so few in number, perhaps because of past exploitation for wood.
Notes. -Homalium leucophloeum was accepted by Sleumer (1973) as a variety of H. albiflorum but is herein reinstated as a species. As for several other segregate species, it is differentiated from H. albiflorum s.s. by its usually 4-merous flowers with glabrous sepal and petal surfaces. Additionally, H. albiflorum has often larger, thin-textured leaves and the flowers are short-pedicellate; its distribution is northern and western, and it occurs at lower altitudes.
The few specimens from the extreme north (DIANA and SAVA regions) have relatively large elliptical, greenish, subentire leaves, sparsely ciliate petals, and in one case larger flowers than any other specimen (extremes of ranges marked with brackets above). These specimens are the only ones in this species or the group of related species that have ciliate petals, and the possibility that they are distinct or, contrarily, reflect some small degree of gene flow from H. albiflorum should be considered. One collection from very high altitude in the southeastern part of the distribution (Rogers 675) is of unusual appearance, with narrow, very long-petioled leaves and numerous racemes; this population may also be genetically distinct. The isotype at P is marked "Emirna" [Imerina] and gives a date of February 1840, rather than just 1840. Its fragmentary nature strongly suggests that it is a duplicate of the holotype, but the inconsistency of labeling may make this uncertain.

Holotypus
Etymology. -Homalium megaphyllum is so named for its exceptionally large leaves.
Distribution, ecology and conservation status. -Homalium megaphyllum is confined to northern Madagascar, primarily the DIANA region (Fig. 2). It is frequently reported to occur along the banks of rivers or streams, including seasonal temporary streams, and once to grow in deep red soil. It has been collected in degraded, or secondary, savoka forests. More than ten probably distinct populations have been collected, and it occurs in the protected areas of Manongarivo, Tsaratanana and Lokobe. Its conservation status is tentatively assessed as "Least Concern" [LC].
Notes. -Homalium megaphyllum is certainly more closely related to H. leucophloeum and H. baillonii than to H. albiflorum s.str., as evidenced by its 4-merous flowers with glabrous sepal and petal surfaces. It has a much larger maximum leaf size than any other species of the section, and is also unique in having most inflorescences borne proximally on mature twigs, rather than in leaf axils.
Etymology. -Homalium phillipsonii is named for Peter B. Phillipson, collector of the type, to honor his many contributions to the botany of Madagascar. Distribution, ecology and conservation status. -Homalium phillipsonii as herein described is native to the Atsimo-Andrefana region of southwestern Madagascar (Fig. 2). [As noted below, there are similar populations in northern Madagascar, but the status of these is doubtful]. It occurs in dry deciduous forest and bush, on sand and rocky limestone substrates. Based on historical collections, the EOO is estimated as 11,806 km2, and the AOO as 72 km2. It appears that more than ten distinct populations have existed. However, in recent decades all collections but one (Razakamalala 6111) have been made in the protected area of Zombitsy. The vast majority of the habitat is unprotected, has suffered severe damage since the time when historical collections were made (with all woody species suitable for use as charcoal virtually extirpated in many areas), and continues to be subject to ongoing anthropogenic damage. Therefore, it is considered very likely that some of the historical populations are now extinct, and that the species should be assessed as "Vulnerable" [VU B2ab(iii)].
Notes. -Homalium phillipsonii is most readily distinguished from H. albiflorum s.str. by the pilose indument of its leaves, twigs, petioles, and portions of the calyx. In H. albiflorum, the pedicels and calyx are occasionally pilose but the leaves, twigs, and petioles, though rarely pubescent, are not pilose. Homalium phillipsonii has more strongly prominent secondary veins than any related species, and more frequently has small structures interpreted as domatia. The inflorescences also seem subjectively to appear thicker and less pendent than those of H. albiflorum, and the anthers are larger and narrower than usual for that species (whose morphology is variable).
Etymology. -Homalium pseudoracemosum is so named because its inflorescences appear on casual observation to be racemose, but are actually paniculate. Wood is used for construction and manufacture of planks (Service Forestier 16408, 26203).
Distribution, ecology and conservation status. -Homalium pseudoracemosum has been widespread in the dry western regions of Madagascar, with a latitudinal range extending from Menabe to Sofia and possibly DIANA (Fig. 2). The two specimens from the DIANA region in the extreme north are atypical and are tentatively placed here. The species is reported to occur on limestone.
Homalium pseudoracemosum has probably occurred in more than ten populations, though locality data are poor in many cases, and in protected areas including the Bemaraha reserve, Namoroka, and (an atypical specimen) Montagne d'Ambre. Therefore, by standard application of the IUCN criteria, its conservation status would be assessed as "Least Concern". However, the fact that only one atypical recent collection exists is of great concern. The case of this species may be compared to that of H. albiflorum, which has a similarly broad western-to-northern distribution, but has been collected from four regions since 1990. From historical data, the EOO of H. pseudoracemosum would be estimated as 140,994 km2 (including the DIANA populations) and the AOO as 72 km2. The vast majority of the potential habitat is unprotected and has been destroyed or severely degraded by human activity since the 1940s and 1950s, when most collections were made. As in the case of H. phillipsonii, it is probable that several of the historically collected populations no longer exist. Therefore, it is suggested that the conservation status of this species should be estimated as, minimally, "Vulnerable" [VU B2ab(iii)] because of the small AOO, presumably fewer than 10 surviving populations, and severe, continuing decline in area and quality of habitat.
Notes. -Homalium pseudoracemosum is distinguished by its short-branched racemiform panicles and lanceolate to ovate or elliptical leaves. Elliptical leaves (as on the atypical Andrianantoanina & Bezara 857) are often at the lower end of the size range, suggesting that they could be immature. The maximum size of the flowers appears to be smaller than in most species of this section, with the petals less strongly accrescent than most. This species occurs in much of the same range as H. albiflorum, which has usually elliptical leaves, usually racemose (though occasionally narrowly paniculate) inflorescences, pubescent rachises and flowers, and usually 5, somewhat larger petals. Homalium albiflorum is the only other species that ever has panicles of this form. The two are suspected to be closely related and to hybridize. However, H. pseudoracemosum also shows possible affinities to the H. leucophloeum group of mostly eastern species in its usually 4-merous, nearly glabrous sepals, petals, and inflorescences. Thus H. pseudoracemosum appears in some ways to represent an intermediate between these species groups.
Species of the H. albiflorum complex are generally described as having white or whitish flowers, when the color is reported, although H. leucophloeum is said to have pale greenish to pale yellowish flowers. Andrianantoanina & Bezara 857, one of the atypical extreme-northern specimens of H. pseudoracemosum, has label data reporting that the calyx is green and the corolla yellow. It is unclear whether this unusual report is due to life stage or differing interpretations of lightly pigmented petals, or whether this species indeed has a significantly different and darker flower color than most of its relatives. If the latter, it would provide another distinguishing feature in the field.
Several specimens appear morphologically intermediate between H. pseudoracemosum and H. albiflorum. Those from Ankarana have quite narrow leaves, inconsistently branched inflorescences with pubescent rachises, and pubescent flowers. Other narrow-leaved specimens possibly representing introgression between the two species are treated above under H. albiflorum. Leandri 356 was probably collected around the same time as Leandri 357, which is identified as H. albiflorum. This specimen has some features that are more consistent with H. pseudoracemosum, including sometimes narrow leaves, usually (but not always) glabrous rachises, and petals glabrous except for cilia. The bracts are cup-shaped and unusually large for either species (a feature also sometimes seen in the Ankarana specimens). No other possible parental species are known from near Bemaraha. 9. Homalium rakotovaoi Appleq., sp. nov. (Fig. 8). Tree to 25 m tall or shrub; twigs dark brown with conspicuous pale lenticels, glabrous. Leaves ovate (lanceolate to elliptical), (5.5 -)6.7 -15.7 × (2.8 -)3.5 -6.5 cm, variably thickish  Etymology. -Homalium rakotovaoi is named for Charles Rakotovao, collector of the type, to honor his many contributions to botany in Madagascar. Distribution, ecology and conservation status. -Homalium rakotovaoi is native to northern Madagascar (Fig. 2). It has been reported to occur in mid-altitude humid forest (though much of the potential range is probably subhumid) and to occur near rivers or on slopes, once on limestone. The EOO is estimated as 3434 km2, and the AOO as 36 km2, with some collections' localities estimated with a low degree of accuracy, but with fewer than ten distinct populations known. Several collections are from various portions of the protected area of Tsaratanana. The conservation status is tentatively estimated as "Least Concern" [LC].
Notes. -Homalium rakotovaoi has usually ovate leaves with often conspicuously crenate to wavy (though sometimes subentire) margins, large clusters of long-pedicellate flowers, narrow acute sepals, and 4-merous flowers that are glabrous or glabrate except for sparse pubescence on the calyx cup, the sepals and petals without ciliate margins. The latter floral characters indicate a closer relationship to the H. leucophloeum group than to H. albiflorum s.s. Most of the species in that group have usually more or less elliptical leaves with often entire margins and flowers in groups of up to 3 or 4, with short pedicels or sessile. Two species, H. rakotovaoi and H. vohitsiandrianense Appleq. (see below), have usually ovate leaves, well-developed pedicels, and flowers sometimes in larger groups (in this species, at the extreme, up to 7). They are presumed to be sister species. Homalium vohitsiandrianense, which is known only from a southeastern massif, has smaller, sometimes broadly ovate leaves with usually acute apices, shorter racemes, and huge sepal glands.
Ranirison & Nusbaumer 914 has large (to over 15 cm long, 8 cm broad), glabrous leaves with often acuminate apices and flowers in clusters of several with well-developed pedicels. However, the leaves are elliptical and it has long-peduncled pubescent inflorescences and large pentamerous flowers with pilose calyces (with unusually long narrow sepals) and pubescent petals. It is plausibly interpreted as a hybrid of H. rakotovaoi and H. albiflorum. Although H. rakotovaoi has not been collected near Daraina, its presence in that region is predicted based on the existence of this intermediate. However, an alternative possibility is that this collection is a distinct, locally endemic species that happens by coincidence to have intermediate morphology. Further collections from Daraina would be desirable.
The wood is reported to be very hard and used in construction (Cours 4437).
Distribution, ecology and conservation status. -Homalium rubriflorum is native to mid-elevation humid forests in the Alaotra-Mangoro region of northeastern Madagascar. The EOO is estimated as 5612 km2, and the AOO as 32 km2. As few as four clearly distinct populations have been collected. Two of these, which supply almost all of the collections, have been widely distributed in the protected areas of Analamazaotra or Perinet (now Andasibe-Mantadia) and Zahamena. Therefore, the species is not expected currently to be experiencing severe declines in available habitat, and its conservation status is estimated as "Least Concern" [LC]. However, it is of concern that the only recent collections have been from a single area, that of Zahamena.
Notes. -Sleumer saw two duplicates of the type collection at P [P00375175, P04734390]. Both sheets were marked by Sleumer as "holotype", but only the former is treated as a type by the Paris herbarium. Since Sleumer did not distinguish between these two sheets in labeling or in print, they are to be treated as syntypes (Art. 40, Note 1 of the ICN; Turland et al., 2018) and one should be chosen as lectotype. The sheet previously labeled as the type is herein designated as lectotype because it is a better specimen and has both the original collector's label and additional material in a fragment packet. be rare. The EOO is estimated as 240 km2, and the AOO as 12 km2 (the three populations are clearly separated, but are arranged in almost a linear pattern, making the calculated EOO low). One collection was made in the protected area of Mananara-Nord. However, most of the habitat is unprotected and continues to suffer anthropogenic damage. Therefore, the estimated conservation status of this species is "Endangered" [EN B1ab(iii)+B2ab(iii)].
Notes. -The holotype of Nisa sanguinea has been reported to be at P (Sleumer, 1973: 301, with the collection number misstated as the year of collection). Since three sheets of the type collection are present at P and no distinction among them has been published, these are syntypes and one must be selected as lectotype. The sheet numbered P04734378 is by far the best, so is chosen here. Two un-numbered Boivin collections at P have been marked as probable or questionable type material, but their status is unclear, and the specimen said to have been cultivated outside Madagascar, in the botanical garden on the island of Bourbon, certainly is not type material. 12. Homalium vohitsiandrianense Appleq., sp. nov. (Fig. 9). Homalium vohitsiandrianense Appleq. differs f rom H. rakotovaoi Appleq. in its smaller, often proportionately broader leaves with acute (to rounded or emarginate) apices, shorter racemes, minute but often dense pubescence on pedicels and calyx cups, and very large sepal glands.
Distribution, ecology and conservation status. -Homalium vohitsiandrianense is known only from a single 1955 collection on the southeastern massif of Vohitsiandriana (Fig. 2). The potential habitat will have been substantially reduced in the following 64 years by anthropogenic damage. If the population still exists, the appropriate assessment of its conservation status is "Critically Endangered" [CR B1ab(iii)+B2ab(iii)].
Notes. -Though H. vohitsiandrianense is known only from the type, it is quite distinct from other species occurring in the region. It is notable for its ovate leaves, racemes with flowers often in clusters of up to 5, long pedicels, broad sepals, and very large sepal glands. The plant is mostly glabrous except for minute, almost long-papillate, but often dense pubescence on the pedicels and calyx cup. It is presumed to be the sister species of H. rakotovaoi, a northern species that shares usually ovate leaves and 4-merous, long-pedicelled flowers often borne in clusters of several. That species has larger, proportionately narrower leaves, longer racemes, and much smaller sepal glands.