Exodeconus maritimus

Rodriguez, Ivana, 2000, Flower anatomy and morphology of Exodeconus maritimus (Solanaceae, Solaneae) and Nicandra physalodes (Solanaceae, Nicandreae): importance for their systematic relationships, Adansonia (3) 22 (2), pp. 187-199 : 189-191

Exodeconus maritimus

Calyx

The sepals are triangular, overlaping up to half of their length, 5.5-6.5 mm long and 1.5-1.8 mm wide. Trichomes vary considerably: eglandular, simple, pluricellular, and glandular with spherical unicellular or elipsoidal head ( Fig. 1A,B ), and are located over the external face of the sepals. Anatomically, the calyx is formed by two epidermises, with a thick cuticle, and five to six layers of parenchymatous tissue ( Fig. 2D ). These cells are isodiametric in cross sections leaving reduced spaces among them ( Fig. 2D ). Chloroplasts and starch are usually observed in the parenchyma cells.

Corolla

The shape is tubular-infundibuliform; it is white, with a violet throat, 17-18 mm long and 4.5-6.5 mm wide. The anatomical structure is very similar to the calyx, with slight differences: the petals’ epidermis is covered by a thin cuticle, and the parenchyma cells possess a large lumen. — Fig. 2D,F .

Androecium

The filaments are pubescent at the base with simple eglandular trichomes ( Fig. 1A,C ), and are composed of an epidermis, parenchymatic tissue, and a single vascular strand. The length of filaments is distinctive; three filaments are shorter than the other two ( Fig. 1C ). The anthers are small (3.2-3.5 mm), glabrous, and formed of a simple epidermis and an endothecium constituted of two cell strata with fibrous thickenings ( Fig. 1D,F ). Dehiscence occurs at the stomium ( Fig. 1D,E ), which is formed by a layer of seven to ten cells with crystalline sand. After dehiscence, the walls disorganize, and their contents are leaked into the lysigenous cavity they form ( Fig. 1D,E,G ). Andro-sterility is observed in E. maritimus , where the flowers display two or three sterile anthers ( Fig. 1G ). The pollen sacs possess normal endothecium, collapsed tapetum and empty pollen grains ( Fig. 1G ).

Gynoecium

The stigma is depressed and enlarged toward its flanks, giving it a fan-like shape ( Fig. 3A ). The receptive surface is covered by unicellular papillae enlarged at the base and rounded towards the apex ( Fig. 3B,C ). The style bears eglandular, simple, pluricellular trichomes and stomata shared on the epidermis ( Fig. 3B,D ). The ovary is ringshaped in cross section ( Fig. 2D,F ), bicarpellar, with 4 locules at the base due to the false septa ( Fig. 2D ). This characteristic disappears at the apex of the ovary ( Fig. 2F ). Crystalline sand is frequently found in the parenchymatic tissue of the ovary. The nectary, located at the base of the ovary ( Fig. 2A ), has the shape of a ring with two swellings at opposite sides and at the level of the septa ( Fig. 2A ,C-E). The secretory tissue is constituted by 5-6 layers of isodiametric cells with large nuclei and vacuolated cytoplasm ( Fig. 2D ). Also, there are 12-15 layers of cells ( Fig. 2D,E ) and 20 ± 3 stomata concentrated at the upper part of the nectary swellings ( Fig. 2B ). The secre- tory tissue is supplied by two dorsal and several lateral vascular bundles that ascend to the external wall of the ovary ( Fig. 4A,H ).

Vascularization

The peduncle shows a siphonostele, which divides into 10 vascular bundles forming a circle ( Fig. 4 A-C). Five traces split to constitute the main sepal bundles, which give rise to lateral ramifications ( Fig. 4A ,D-F). The five remaining vascular bundles are reorganized, acquiring a star shape ( Fig. 4A,E,F ). Five main corolla bundles are immediately formed taking an external position (each one produces two or three lateral ramifications). The five staminal bundles acquire an internal position ( Fig. 4A,G ). After these divisions, the remaining vascular tissue is reordered in a circle, entering the gynoecium ( Fig. 4A,G,H ). The ovary has 2 or 4 ventral vascular bundles in the central region ( Fig. 4A,H ); when 4, they then decrease to only 2 by fusion at the level of the apical portion of the ovary ( Fig. 4A,I,J ). The dorsal vascular bundles enter the style, reaching the base of the stigma without ramifications ( Fig. 4A,K,L ).

Figures

Fig. 1. — Exodeconus maritimus, androecium and flower trichomes: A, eglandular trichome; B, glandular trichome; C, stamens; D-F, cross section of anther, details of the stomium and endothecium; G, cross section of anther with sterile pollen sacs. Scale bars: A, B = 2 µm; C = 3 mm; D, G = 800 µm; E, F = 10 µm. Abbreviations: e = endothecium; c = crystals; s = stomium.

Fig. 2. — Exodeconus maritimus, ovary: A, B, ovary, nectary, and their stomata (SEM); C, longitudinal section of ovary; D-F, cross section at different levels of the ovary. Scale bars: A = 200 µm; B = 50 µm; C, D, F = 800 µm; E = 100 µm. Abbreviation: n = nectary.

Fig. 3. — Exodeconus maritimus, stigma: A, B, stigma and stigmatic papillae (SEM); C, longitudinal section of stigmatic surface; D, stoma. Scale bars: A = 100 µm; B = 50 µm; C = 10 µm; D = 5 µm. Abbreviation: p = unicellular papilla.

Fig. 4. — Exodeconus maritimus, flower vascularization: A, longitudinal section of mature bud, along plane indicated in H; B-L, cross sections from peduncle to apex, as indicated in A. Symbols: Blackened areas, vascular tissue; gray areas, nectary; diagonal lines, transmitting tissue. Abbreviation: d, dorsal vascular bundles; e, staminal bundle; lc, lateral petal bundle; lk, lateral sepal bundle; lo, lateral ovarian bundle; mc, median petal bundle; mk, median sepal bundle; vc, ventral vascular bundle. Scale bars: for Fig. A is a; for Figs. B-L is b.