Glandonia Grisebach, 1858

Guesdon, Isabel Reis, Amorim, André Márcio & Meira, Renata Maria Strozi Alves, 2018, The hydrochorous Amazonian genus Glandonia (Malpighiaceae): new records, morphoanatomy updates and taxonomic contributions, Phytotaxa 345 (1), pp. 13-25 : 14-20

Glandonia Grisebach in Martius, Flora Brasiliensis 12(1): 23. 1858.

Type: — Glandonia macrocarpa Griseb.

Trees or small trees. Leaf blade with glands on the abaxial surface; stipules linear, interpetiolar, caducous. Inflorescence a raceme of cincinni, erect, terminal; bracteoles bearing a gland on the abaxial surface. Sepals five, each with two glands. Outermost petal helmet-shaped, all lateral petals white and reflexed; posterior petal yellow, limb reflexed or not, with flattened marginal glands. Filaments very short and densely hirsute; locules of anthers bearing linear projections. Ovary tricarpellate. Fruit indehiscent, dry when mature, monospermic (2 locules collapsed).

Biogeographical comments— Our field records and most herbarium collections corroborate the geographical distribution of Glandonia reported by Anderson (1981) ( Fig. 1 ). One of the hypotheses to explain the high endemism in Amazonian flooded areas is the isolation of biota in refuges during arid periods of the Pleistocene ( Prance 1982). Anderson (1981) noted the disjunct distribution of Glandonia species, G. williamsii from the upper Rio Negro and Orinoco, G. macrocarpa from the lower Rio Negro and G. prancei from the upper Rio Purus and Rio Madeira. However, the atypical specimens of G. macrocarpa from upper Rio Negro and the recent record of G. prancei from the Lower Rio Purus suggest the lack of new records is a consequence of the little collection effort in areas that are difficult to access.

Morpho-anatomical comments— Each species of Glandonia is easily distinguished from each other ( Table 1). Glandonia species differ in leaf shape, being elliptical to slightly obovate. Only G. macrocarpa has a strongly obovate leaf. The base of the leaf blade is typically cuneate, while it is rounded in G. williamsii ( Fig. 2 ; 3D–F ). The joint portion of the pedicel in G. prancei and G. williamsii is very distinct from the floriferous peduncle ( Fig. 3J ). Similar to Anderson (1981), we noticed the stipules split during development. In addition, we noticed that inflorescences are typically erect ( Fig. 3B, C ), that the color of glands can vary among the species ( Fig. 3D–K ), and that only G. williamsii has a keel-shaped leaf ( Fig. 3A ). The size and position of the petals, as well as the shape of mature fruits differ among the species.

The anatomical studies helped us to elucidate the presence of leaf glands. In general, there are two to four basilaminar leaf glands in Glandonia macrocarpa and G. williamsii , while in G. prancei there are only two glands. Smaller laminar leaf glands scattered throughout the blade are conspicuous in G. williamsii ( Fig. 4I ), which are easily seen with the naked eye, while in G. macrocarpa and G. prancei they are inconspicuous ( Fig. 4J ). Leaf glands were also mentioned in the treatment by Anderson (1981); however, details about position and size were not reported.

The leaf blade anatomy of Glandonia revealed characters commonly found in Malpighiaceae species, as reported by Araújo et al. (2010) and Almeida et al. (2017), including dorsiventral mesophyll with a single layer of palisade parenchyma and paracytic stomata ( Fig. 4B, E ). One of the most distinctive characters of the leaf epidermis is the presence of cylindrical papillae, which only occur on the abaxial surface of G. williamsii leaves ( Fig. 4C–E ).

The pattern of the petiole’s vascular system in is an important diagnostic anatomical character and is easily observed in transverse section. A vascular bundle arranged as a curved arc with invaginated ends with accessory vascular bundles was recorded in Malpighiaceae species surveyed by Araújo et al. (2010) and Almeida et al. (2017). This was observed in G. prancei ( Fig. 4G ) and G. williamsii , whereas the petiolar central bundle of G. macrocarpa is arranged as a concentric arc ( Fig. 4H ).

Sclereids were encountered throughout the leaf, mainly in the cortex of the midrib ( Fig. 4F ). This is the first record of sclereids in Malpighiaceae flowers. These cells were found in the outermost petal of all Glandonia species, in the calyx and in posterior petal of G. williamsii ( Fig. 4M–O ); the sclereids probably help the posterior petal blade stand erect.

The leaf and bracteole glands are typical nectaries; composed of palisade-like secretory epidermis, vascularized parenchyma and secretion of nectar (Guesdon et al. unpublished data). Our study represents the first of bracteole glands anatomy in the family.Additionally, the secretory surface of bracteole glands provides distinctive character ( Fig. 4K, L ), being exclusively flat in G. prancei . The posterior petal glands are dorsoventrally flattened, contrasting with digitiform petal glands describe by Possobom et al. (2015); the number and size of these glands distingue the Glandonia species ( Fig. 5A–I ). Guesdon et al. (unpublished data) have studied the morpho-anatomy and histochemistry of petal glands in Glandonia species and noticed its similarity with oil-producing sepal glands, classified as elaiophores by Vogel (1990). However, these petal structures probably act as osmophores ( Possobom et al. 2015). The anatomical data collected during this work are promising for taxonomic and phylogenetic studies in Malpighiaceae .

Key to the species of Glandonia (adapted from Anderson, 1981)

1. Leaf coriaceous, abaxial surface papillose, with conspicuous glands throughout the leaf blade, basilaminar glands ca. 1.5 mm diameter and laminar ca. 0.8 mm diameter; posterior petal with about 18 marginal glands on the proximal portion of the limb, ca. 0.1 × 0.2 mm, sclereids present in posterior petal limb; apex of mature fruit slightly acute .......................................... G. williamsii

- Leaf papyraceous, abaxial surface not papillose, with conspicuous glands restricted to the base of the leaf blade; posterior petal with 5–12 marginal glands on the proximal portion of the limb, sclereids absent from the posterior petal limb; apex of mature fruit truncate ............................................................................................................................................................................................... 2

2. Leaf strongly obovate, with (0)2–4 basilaminar leaf glands (yellow), glands ca. 1.3 mm diameter; bracteole glands (creamy white) with convex secretory surface; petiolar vascular system arranged as an concentric arc; floriferous peduncle ca. 1–2 mm long; joint of pedicel little or not distinct from peduncle, pedicel 10–15 mm long; posterior petal with ca. 5–9 marginal glands on the proximal portion of the limb, ca. 1 × 0.4 mm ............................................................................................................................. G. macrocarpa

- Leaf elliptical or rarely slightly obovate, with (0)2 basilaminar leaf glands (white), glands ca. 0.5 mm diameter; bracteole glands (white) with truncate secretory surface; petiolar vascular system arranged as a curved arc with invaginated ends; floriferous peduncle ca. 2–4.8 mm long; joint of pedicel very distinct from peduncle, pedicel 6–8.3 mm long; posterior petal with ca. 12 marginal glands on the proximal portion of the limb, ca. 0.3 × 0.3 mm ............................................................................ G. prancei

Figures

FIGURE 1. A. Map showing the distribution of Glandonia macrocarpa (black triangles), G. prancei (black circles) and G. williamsii (black squares). B. Glandonia macrocarpa specimen (arrow) in terra firme forest. C. Glandonia williamsii specimen (arrow) in igapó. D. Hydrochorous fruit of G. prancei.

FIGURE 2. General view of Glandonia species: A and B Glandonia macrocarpa: A. Flowering branch, B. lateral and frontal view of fruit. C. Fruiting branch of G. williamsii. D. Fruiting branch of G. prancei. Drawing A from Guesdon 16 (INPA), B from Ducke 793 (INPA), C from Fróes 28782 (MG) and D from Prance et al. 20557 (INPA).

FIGURE 3. Vegetative and reproductive characters of Glandonia species: A. keel-shaped leaves of G. williamsii, B. and C. general view of leaves and inflorescence of G. prancei. Basilaminar leaf glands: D. Glandonia macrocarpa, E. Glandonia prancei and F. Glandonia williamsii. Laminar leaf glands: G. Glandonia williamsii and H. Glandonia macrocarpa. Floral glands: I. bracteole gland (BG) of G. macrocarpa, J. bracteole and sepal glands of G. prancei (BG and SG, respectively), black arrow: pedicel joint. K. Posterior petal in bud of G. macrocarpa, note the petal glands (arrow) L. Helmet-shaped petal (HP) and reflexed limb of posterior petal (PP) in G. macrocarpa.

FIGURE 4. Anatomical characters of Glandonia species. A. Adaxial surface of G. macrocarpa showing indument scars (black arrow). B. Abaxial surface of G. prancei showing a stoma (black arrow) and sinuous outline of the anticlinal epidermal wall. Abaxial surface of G. williamsii C. papillae covering a stoma (black arrow), D. papillose surface (SEM image), a stoma (white arrow). E. Transversal section of leaf of G. williamsii, papillae (white arrow), F. Sclereids in midrib of G. macrocarpa (black arrow). Diagrammatic schemas of petiolar vascular systems G. a curved arc with invaginated ends in G. prancei and H. a concentric arc delimiting a central pith in G. macrocarpa, dot-filled areas: phloem, striped areas: xylem. Leaf blade cleared I. in G. williamsii and J. in G. prancei, note the laminar gland (arrow). Transversal view of bracteole gland K. convex surface in G. macrocarpa, L. truncate surface in G. prancei. M–O. Sclereids on posterior petal of G. williamsii, N. Macrosclereids, O. Brachysclereids.

FIGURE 5. Morphoanatomical floral characters of Glandonia species. A–C: Glandonia macrocarpa: A. General view of the flowers, B. Posterior petal margin (SEM image) and C. Posterior petal cleared. D–F: Glandonia prancei: D. General view of the flowers, E. Posterior petal margin (SEM image) and F. Posterior petal cleared; G–I: Glandonia williamsii: G. General view of the flowers H. Posterior petal margin (SEM image) and I. Posterior petal cleared. PP: Posterior petal. SG: Sepal glands. BG: Bracteole gland.