Polygonum schischkinii

Yurtseva, Olga V., Severova, Elena E., Deviatov, Andrey G., V. Olonova, Marina & Samigullin, Tahir H., 2021, Polygonum schischkinii is a member of Atraphaxis (Polygonaceae, Polygoneae): evidences from morphological and molecular analyses, Phytotaxa 491 (3), pp. 193-216 : 198-203

Morphology of Polygonum schischkinii

Life form and shoots:— Polygonum schischkinii is a subshrub, 20–35 cm tall, branched from the base ( Fig. 1 ). Shoots die annually almost to the base, the remaining basal parts of annual shoots (“resides”) form a many-headed caudex covered with fibrously disintegrated purple-brown bark. Annual shoots are erect, straight, simple or weakly branched, leafy to the top, angulate or ribbed, greenish-gray, glabrous. The shoot is 1.5–3.0 mm in diameter at the base, 1.0– 1.5 mm in diameter at the top. The basal nodes are spaced by the distance 22–25 mm. Leaf blades gradually reduce their size towards the top of the shoots.

Thyrses:— Terminal frondulose thyrses include 7–13 cymes of 1–2 flowers in the axils of bracts, which are represented by linear leaf blades and ocreas, or only ocreas. The lower cymes in the thyrse are spaced by internodes 10–12 mm long, the upper internodes are reduced to 2–5 mm ( Fig. 1 ).

Leaf blades:— Bottom leaf blades are obovate or broadly elliptical, 14–23 × 5–10 mm, apex obtuse or shortly pointed, base cuneate, tapered into a petiole 2.0– 2.5 mm long joint to the ocrea with articulation ( Figs. 2A–B ; 3A ), glaucous, thick, leathery, glabrous, slightly revolute at the margins, with a midvein visible on the abaxial side. Upper leaf blades are reduced to (2)10–12 × 1 mm, linear ( Figs. 3H ; 4A ). The surface of leaf blade is covered with convex rounded cells alternating with stomata ( Fig. 4B–C ), which are more numerous on the lower side ( Fig. 4D ). The epidermal cells are covered with wax crystals in the form of flakes, needles and plates ( Figs. 4E–F ).

Ocreas and ocreolas:— Vegetative shoots have ocreas 7–12 mm long, lanceolate-tubular, brown at the base, above whitish, membranous, later longitudinally split in two lateral lanceolate lacinulas 5–8 mm long, each with a yellowish vein, and a middle lobula 1.0 × 1.0–2.0 mm, truncate and finely serrate-incised at the top ( Figs. 2C–D ; 3B–D , and F). In thyrses, the low ocreolas are 3–4 mm long, lanceolate-tubular, subsequently split into two lateral lanceolate lacinulas 1.5–3.3 mm long, each with a yellowish vein, and a middle lobula 1.0 × 1.0 mm finely serrateincised at the top ( Figs. 2E–F ; 3E ). The upper ocreolas are lanceolate, membranous ( Fig. 3G ).

Perianth morphology:— The perianth is 3.0– 3.5 mm long in flowering and 4.0 mm long in fruiting, campanulate, glabrous, divided to 5/ 6 in five equal-sized oblong-elliptical tepals 2.0–2.5 × 1.0– 1.2 mm ( Figs. 2G–H ; 3H–J ). The tepals are flat, greenish-purple along the midveins, with pinkish margins papillate at the edges ( Figs. 2I ; 5B–C ). The perianth tube is funnel-shaped, 1.0– 1.2 mm long, gradually narrowed to a filiform basal part 0.2 mm long articulated to a pedicel 0.7–1.5 mm long ( Figs. 3H–J and 4G ).

Perianth surface:— The epidermal cells covering the tube and the bases of the tepals externally are rounded or elongate-rectangular, with convex or flat outer walls bearing irregular cuticular striations ( Fig. 4H–J ). The epidermal cells covering the tepals abaxially are irregular or sinuate in outline, with flat outer periclinal walls bearing fine irregular cuticular striations ( Figs. 4L and 5A–B ).Adaxially, the epidermal cells of the tepals bear longitudinal striation. Numerous stomata are randomly scattered across the tepals along the midveins abaxially ( Figs. 4A, K ), but are absent from the petaloid tepal margins ( Figs. 4L ; 5A–B ). The cells of the tepal edges form papillae 20–30 µm long, 5–7(–10) µm in diameter with a tightly pressed longitudinal striation ( Fig. 5B–C ).

Receptacle and stamens:— The perianth tube is formed by fused bases of tepals and could be also interpreted as a concave receptacle. Eight stamens in two whorls have flattened bases of the filaments, which are inserted at the base of the receptacle and are slightly fused to it adaxially. The filaments of the five outer stamens are lanceolate-subulate, gradually dilated to the base, 1.0– 1.2 mm long and half the length of the tepals. The filaments of three inner stamens are 1.5 mm long, strongly expanded at 2/3 of the length and gradually narrowed to the top ( Fig. 5D ). The filaments of outer stamens are inserted higher than the inner stamens at the receptacle. The inner surface of the receptacle and the basal parts of the filaments (2/3 of the length) are lined by smooth nectar-secreting tissue ( Fig. 5D–F ). The upper parts of the filaments (1/3 of the length) are covered with elongate-rectangular cells with irregular cuticular striations, which resemble the epidermal cells covering the tepals abaxially ( Fig. 5G ). Anthers are orbiculate, dark-pink.

Styles:— Three (rarely two) styles 0.45–0.50 mm long are fused at the base forming a beak-shaped apex of the fruit 0.6 mm long. The styles are linear throughout the length ( Fig. 2I ) and covered with oblong-rectangular cells with longitudinal cuticular striations.

Fruit morphology and surface:— The fruits are narrowly ovoid, trigonous (rarely lenticular), with distinct ribs and convex sides. Premature fruits are included in the persistent perianth, light-brown, smooth, shiny, 2.4–2.5 × 1.3 mm ( Fig. 2H–I ), mature achenes are dark-brown, 3.0–4.0 × 1.5 mm ( Fig. 3J ). The surface of premature fruit is formed by the exocarp cells sinuate in outline and divided by narrow grooves ( Fig. 5H–I ). The mature fruit has smooth surface and is exserted from the perianth to 1/4–1/3 of the length ( Fig. 3J ).

Pericarp anatomy:— We studied the pericarp anatomy of unripe and ripe fruits ( Fig. 6 ). In cross section, the unripe fruits are triangular, with distinct, almost winged ribs and concave sides ( Fig. 6A ). The pericarp 75–80 µm high includes one-layered exocarp, several layers of parenchymatous mesocarp and 1–2 layers of endocarp, the latter is obliterated in ripe fruits. In cross section, most of the pericarp height is represented by exocarp cells 60–65 µm high in the sides and 50–70 µm high in the ribs ( Fig. 6B–D ). The ribs are formed by fused inverted sides, so that the exocarp layers are connected by mesocarp including a vascular bundle which consists of a few phloem and xylem elements ( Fig. 6A ).

In cross section, the exocarp cells of unripe fruit ( Fig. 6B–C ) have almost straight anticlinal walls, which become thicker to periphery, so the walls dividing adjacent lumina are 8–10 µm wide. In the fruit sides, the lumina are rectangular, 20–30 µm wide ( Fig. 6B ). In the ribs the lumina are 10 µm wide at the base and 25–30 µm at the periphery ( Fig. 6C ). External periclinal wall is 3–4 µm thick, strongly undulates and forms invaginations and protrusions ( Fig. 6B–C ). Later the adjacent invaginations merge, providing quick thickening of the external periclinal wall. Narrow channels between the loops of the external wall go to the surface. The fruit surface is covered with a cuticle 1 µm thick which becomes thicker in ripe fruit. The walls of unripe fruits are not lignified, the walls and content of the exocarp cells are light brown.

In ripe fruits, the anticlinal walls of exocarp cells strongly undulate ( Fig. 6D ), the external periclinal walls preserve invaginations and protrusions, but become thicker. The channels between the invaginations are dendritically branched. In ripe fruits, the lumina of exocarp cells are two times thinner ( Fig. 6D ) than in unripe fruits ( Fig. 6B ). In ripe fruits the walls and the content of the exocarp cells are slightly lignified and colored dark-brown due to the presence of phlobaphens.

In surface view, the exocarp cells are polygonal in ovary and strongly sinuate in outline in unripe fruits ( Fig. 5H ). The external periclinal wall of unripe fruit has irregular relief formed by invaginations and protrusions of the wall. In ripe fruits the surface becomes smooth.

Pollen:— Polygonum schischkinii has oblong-spheroidal pollen grains 24.2–27.3 × 19.3–20.7 µm (P/E = 1.29); tricolporate, elliptical in equatorial view, rounded-trilobed in polar view; colpi are distinct, long and deep; ora distinct, lalongate or circular ( Fig. 5J–L ). The sporoderm ornamentation is microreticulate-foveolate, with 4–6-angular pits ca 1.0 µm in diameter, sharply outlined at the edges and including singular pits or rarely perforations ca 0.1–0.2 µm in diameter ( Fig. 5L ). Exine is 2.0 (1.7–2.4) µm thick.

Figures

FIGURE 1. Lectotype of Polygonum glareosum: [CHINA, Xinjiang] Western Mongolia, left bank of the Cherny [Kara] Irtysh River to the East of Mt. Cherek-Tas [Charykty, Saur Mts], sandy-pebble steppe. June 12, 1914. B.K.Schischkin (LE 1013261).

FIGURE 2. Morphology of Polygonum schischkinii: A, B—leaf blade adaxially and abaxially; C–D—ocrea in vegetative zone of the shoot; E—ocreola, view from the side of leaf blade (removed). F—ocreola split it two lateral lacinulas and a short middle lobula, view from the side opposite to leaf blade; G, H—perianth with a fruit inside; I—linear styles at the top of the fruit. Scale bar = 1 mm.

FIGURE 3. Morphology of Polygonum schischkinii: A—leaf blade abaxially; B–D—ocrea at the base of the shoot (B, D—with removed leaf blade); E, F—ocreola and ocrea split in two lateral lacinulas and a serrate-incised middle part, viewed from the side opposite to leaf blade; G—upper part of a thyrse with 1–2 flowers in ocreolas; H—one-flowered cyme; I—perianth in blossom; J—mature fruit exerted from the perianth. Scale bar = 10 mm (A–D), 1 mm (E–J).

FIGURE 4. Morphology of Polygonum schischkinii (SEM): A—a flowerbud and a fragment of a bract; B–F—fragments of a bract with stomata adaxially (B–C) and abaxially (D–F); G—place of articulation of perianth tube to a pedicel; H–I—epidermal cells covering perianth tube outside; J—epidermal cells on the tepal base abaxially; K—flowerbud, middle part of the tepal with stomata surrounded by epidermal cells; L—flowerbud, epidermal cell of the tepal margin. Scale bar = 300 µm (A); 30 µm (B–K); 10 µm (L).

FIGURE 5. Morphology of Polygonum schischkinii: A, B—epidermal cells of the tepal margin; C—papillae at the tepal edge; D— filament of the inner stamen fused to a receptacle; E–nectar-secreating tissue covering the base of the filament and the receptacle; F— nectar-secreating tissue covering the base of the filament; G—epidermal cells covering the top of the filament; H, I—surface of premature fruit on the rib (H) and near the top (I); J–L—pollen. Scale bar = 300 µm (D); 30 µm (A–B, E–I); 10 µm (L); 3 µm (C, J–L).

FIGURE 6. Pericarp anatomy of Polygonum schischkinii: A—a premature fruit in a cross section. B—exocarp cells with vast lumina (lum) and straight anticlinal walls (aw) and undulating external periclinal wall (epw) in the side of premature fruit; C—exocarp cells with undulating external periclinal walls (epw) in the rib of premature fruit; D—exocarp cells with narrow lumina (lum), branching dendritically, and undulating anticlinal walls (aw) in the rib of mature fruit. Scale bar = 100 µm (A); 50 µm (B–D).