Mcvaughia W.R.Anderson, Taxon 28: 157. 1979

Almeida, Rafael F., Guesdon, Isabel R., Pace, Marcelo R. & Meira, Renata M. S., 2019, Taxonomic revision of Mcvaughia W. R. Anderson (Malpighiaceae): notes on vegetative and reproductive anatomy and the description of a new species, PhytoKeys 117, pp. 45-72 : 45

publication ID	https://dx.doi.org/10.3897/phytokeys.117.32207
persistent identifier	https://treatment.plazi.org/id/BA6FCF10-E3EB-3709-B614-34617539657C
treatment provided by	PhytoKeys by Pensoft
scientific name	Mcvaughia W.R.Anderson, Taxon 28: 157. 1979
status

Treatment

Type species.

Mcvaughia bahiana W.R.Anderson

Description.

Shrubs to subshrubs, perennial, growing in sandy soils. Branches cylindrical, densely sericeous or lanate-velutinous, generally glabrescent at age. Stipules epipetiolar, completely connate, persistent. Leaves opposite; petiole eglandular; blade bearing 2-many glands abaxially. Thyrsi terminal, pedunculate, many-branched; cincinni alternate to subopposite, 1-14-flowered; bracts persistent; bracteoles persistent, one of them 1-glandular, the other eglandular, gland green in bud turning yellow in anthesis. Flowers zygomorphic; floral buds slightly flattened at middle; pedicel stout, straight in bud. Sepals leaving petals exposed in pre-anthesis, all 2-glandular. Petals bright to golden yellow, glabrous, the anterior two remaining cupped one inside the other; lateral petals with the margin erose; posterior petal bearing several marginal glands. Stamens 7-8, staminodes 2-3 (stamens opposite the posterior-lateral sepals and the posterior petal); filaments glabrous, those opposite the posterior-lateral petals slightly curved towards the apex; connectives inconspicuous; anthers horseshoe-shaped, glabrous, outer locules confluent at apex, reduced to antherodes in staminodes. Ovary 3-carpellate, 3-locular, 2 locules ± anterior, apparently collapsed lacking ovules, 1 locule almost posterior, fertile, 1-ovulate; styles 3, slender, truncate to uncinate at apex; stigma minute, lateral. Drupes rugose, twisted, asymmetric, 1-locular, proximal chamber thick-walled, 1-seeded, distal chamber thin-walled, filled with a viscous secretion (allowing the fruit to float and to be dispersed by water).

Etymology.

The epithet pays tribute to Dr. Rogers McVaugh (*1909-2009†), an American botanist, expert in the Mexican flora.

Distribution.

Mcvaughia is restricted to sandy soils within sedimentary basins of Northeastern Brazil, with different species being endemic to each sedimentary basin: Mcvaughia bahiana - Tucano basin, M. piauhiensis - Parnaiba basin, and M. sergipana - Sergipe-Alagoas basin ( Amorim and Almeida 2015). Sedimentary basins represent conspicuous phytogeographic zones within the Caatinga domain, with a distinct biota from other areas of Caatinga over crystalline shield, holding endemism records for some angiosperm families ( Cardoso and Queiroz 2007; Almeida et al. 2018; Silva and Souza 2018).

Biogeography.

Mcvaughia is the sister-group of Burdachia and Glandonia , comprising a lineage ( Mcvaughia clade) of early diverging Malpighiaceae with water-dispersed fruits, most commonly found growing along wetland floodplains and upland forest throughout the Amazon Basin ( Anderson 1981). Davis et al. (2014) estimated that the ancestor of this clade might have arisen around 38.0-33.9 Myr, and its extant lineages diversified from 25 to 15 Myr. The description of M. piauhiensis corroborates the hypothesis of Amorim and Almeida (2015) that extant lineages of Mcvaughia have probably experienced recent radiations along the caatingas and restingas of Northeastern Brazil. This inference is based on the fact that all three Mcvaughia species occur along current or past courses of the São Francisco river (SFR): M. piauhiensis occurs to the west, and M. bahiana and M. sergipana occur to the east near the SFR’s delta (Fig. 11 View Figure 11 ). During the upper Pliocene, the SFR flowed to the equatorial Atlantic Ocean via the Piauí or Canindé Rivers, in the Parnaiba river basin, state of Piauí ( King 1956; Nascimento et al. 2013). However, the rising of the Grande and Ibiapaba Ridges in northwestern Ceará state during the Pliocene/Pleistocene boundary would have abruptly interrupted the SFR’s course ( King 1956; Mabesoone 1994; Nascimento et al. 2013; Almeida et al. 2018). By this time, the ancestor of Mcvaughia might have already been established in this area, and its populations might have been isolated from each other by the formation of several lakes in northwestern Bahia, due to the interruption of the river flow ( King 1956; Mabesoone 1994; Nascimento et al. 2013). It was not until the Mindel glaciation (ca. 450.000 years ago) that the SFR found its way to the eastern Atlantic Ocean, bordering the states of Alagoas and Sergipe ( King 1956; Mabesoone 1994; Nascimento et al. 2013), thus, paving the way for recent vicariant cladogenesis events within these populations.

Wood Anatomy of Mcvaughia sergipana .

Heartwood and sapwood indistinct light brown; grain straight to slightly wavy. In anatomical sections, the heartwood appears with abundant cell contents (bottom of Fig. 1 A–B View Figure 1 ) in vessels and other cell types. The contents stain in blue with safrablau (Fig. 1 A–B View Figure 1 ). Growth ring boundaries are distinct (Fig. 1 A–B View Figure 1 ), marked by a line of axial parenchyma (Fig. 1B View Figure 1 ) and thicker walled, radially narrow fibers (Fig. 1 A–B View Figure 1 ). Wood is diffuse-porous (Fig. 1A View Figure 1 ). Vessels are narrow, 34 ± 9 μm, generally arranged in radial multiples of 4 or more (Fig. 1A View Figure 1 ), abundant, 244 ± 57 vessels/mm2, and with a mean length of 365 ± 73 μm. Some solitary vessels and shorter radial multiples are also present (Fig. 1 A–B View Figure 1 ). Perforation plates are simple. Intervessel pits are alternate, minute, 4 μm, vestured. Vessel ray-pitting with distinct borders; similar to intervessel pits in size and shape. Fibers very thick-walled (Fig. 1 A–B View Figure 1 ), with simple to minutely bordered pits. Axial parenchyma paratracheal, scanty and forming a discontinuous line at the growth ring limits (Fig. 1 A–B View Figure 1 ), 3-4 cells per parenchyma strand (Fig. 1C View Figure 1 ). Rays with 1-3 cells wide (Fig. 1C View Figure 1 ), lower than 1 mm (Fig. 1C View Figure 1 ), heterocellular mixed, with procumbent, square and upright cells mixed throughout the ray (Fig. 1C View Figure 1 ). Perforated ray cells common, non-storied (Fig. 1C View Figure 1 ). Large prismatic crystals in enlarged ray cells (Fig. 1C View Figure 1 ) of the body and margins.

Secondary phloem anatomy of Mcvaughia sergipana .

Growth rings are indistinct, phloem non-stratified (Fig. 2 A–C View Figure 2 ). Conducting phloem represents a narrow band of 11-12 cells away from the cambium. Nonconducting phloem is marked by the collapse of the sieve tubes, a more significant dilatation of the axial and ray parenchyma (Fig. 2 A–B View Figure 2 ), and belated sclerosis of some scattered ray cells. Sieve tubes are diffuse (Fig. 2C View Figure 2 ), solitary or in radial multiples of 2 cells (Fig. 2C View Figure 2 ), sieve plates are simple, slightly inclined, 441 ± 71 μm 2 in area (24 ± 2 μm in diameter). Sieve tube elements length is 243 ± 45 μm. Slime plug always evident at the sieve plates. One to two companion cells per sieve tube element, as seen in transverse section. When two companion cells are present, one lies on each side of the sieve tube. Dilatation due to cell expansion and division is evident in the rays, axial parenchyma, and the cortex (Fig. 2 A–B View Figure 2 ). Axial phloem parenchyma constitutes the ground tissue (Fig. 2 A–C View Figure 2 ), four cells per parenchyma strand. Axial parenchyma with druse crystals appears as diffuse-in-aggregate lines (Fig. 2 A–C, E View Figure 2 ), giving a stratified appearance to the phloem, clear both in transverse and radial section (Fig. 2 A–C, E View Figure 2 ). Rays with a straight course, slightly dilated (funnel-shaped). Ray width, height, and composition equal to those of secondary xylem (Fig. 2 D–E View Figure 2 ). Sclerenchyma is represented by scattered bulky fiber-sclereids (Fig. 2 A–C View Figure 2 ) and a few sclerified ray cells in the nonconducting phloem (Fig. 2B View Figure 2 ). Phloem elements are non-storied. Druses are abundant, present in absolutely all parenchyma cells (Fig. 2C View Figure 2 ). Crystals are present both in chambered axial parenchyma cells (Fig. 2C View Figure 2 ) and in individual axial and ray parenchyma cells of the phloem (Fig. 2D View Figure 2 ) and cortex.

Leaf anatomy.

The leaf anatomy in the species of Mcvaughia is quite similar. The vascular system of petioles is arranged as a curved arc with two conspicuous accessory bundles. The most distinctive leaf character is the distribution pattern of glands (Fig. 3 A–C View Figure 3 ). These glands are distributed at the base and throughout the leaf blade, varying in number from two to eight basilaminar glands and from few to several distal laminar glands. The basilaminar and laminar leaf glands were identified as short-stalked (Fig. 3 D–E View Figure 3 ), except in M. sergipana which were recognized as sessile and partially set in the mesophyll (Fig. 3F View Figure 3 ). Based on the anatomical arrangement, these leaf glands are composed of a palisade-like secretory epidermis and vascularized parenchyma (Fig. 3F View Figure 3 ). The laminar glands in M. sergipana are conspicuous (Fig. 3G, I View Figure 3 ), while in M. bahiana (Fig. 3H View Figure 3 ) and M. piauhiensis (Fig. 3J View Figure 3 ) these glands are inconspicuous, and difficult to see with the naked eye. The leaf blade anatomy revealed a dorsiventral mesophyll with a single layer of palisade parenchyma and a variable number of spongy parenchyma layers. In M. sergipana the spongy parenchyma has several layers (Fig. 3K View Figure 3 ), while in M. bahiana and M. piauhiensis fewer layers were observed (Fig. 3L View Figure 3 ). Idioblasts containing druses are commonly observed in the mesophyll (Fig. 3L View Figure 3 ). Malpighiaceous trichomes were observed in the epidermis of both surfaces (Fig. 3 M–O View Figure 3 ), being more abundant abaxially and in young leaves. The outline of the anticlinal epidermal cell walls adaxially is straight (Fig. 3 M–N View Figure 3 ), while abaxially may vary from straight to sinuous (Fig. 3 P–Q View Figure 3 ), being exclusively straight in M. sergipana . All species of Mcvaughia show hypostomatic leaves (Fig. 3 K–L View Figure 3 ), with paracytic stomata (Fig. 3 P–Q View Figure 3 ).

Floral anatomy.

Observations during field trips revealed that sepal and petal glands are yellow in M. sergipana and M. bahiana (Fig. 4 A–B View Figure 4 ). The bracteole gland is initially green (Fig. 4A View Figure 4 ) turning yellow during anthesis. The secretory surface of the bracteole gland may vary from flattened (Fig. 4D View Figure 4 ) in M. sergipana to convex in the other two Mcvaughia species (Fig. 4 E–F View Figure 4 ). The bracteole glands show an anatomical arrangement similar to that of the leaf glands, with palisade-like secretory epidermis and a vascularized secretory parenchyma (Fig. 4G View Figure 4 ). The calyces are particularly zygomorphic, due to the lateral displacement of glands in the anterior sepal (Fig. 4 H–I View Figure 4 ). The bracteole glands are subsessile (Fig. 4 D–F View Figure 4 ), while the sepal glands are short-stalked (Fig. 4J View Figure 4 ). Petal glands were recorded throughout the limb margin of the posterior petal in M. sergipana (Fig. 4K View Figure 4 ) and distributed only at the base in M. bahiana (Fig. 4L View Figure 4 ) and M. piauhiensis . In Mcvaughia sergipana the petal glands at the apex region are sessile (Fig. 4 M–N View Figure 4 ). The basal petal glands in M. bahiana (Fig. 4 O–P View Figure 4 ) and M. piauhiensis are sessile to slightly subsessile (Fig. 4Q View Figure 4 ), while in M. sergipana are stalked (Fig. 4 R–S View Figure 4 ). The petal glands show the same anatomical composition as the leaf, bracteole, and sepal glands (Fig. 4T View Figure 4 ).