Structural Anatomical Aspects of Two Euphorbia (Euphorbiaceae Juss.) Species Leaves

Anallelle Uniiversiităţiiii diin Craiiova, seriia Agriiculltură – Montanollogiie – Cadastru (Annalls of the Uniiversiity of Craiiova - Agriicullture, Montanollogy, Cadastre Seriies) Voll. XLIX/2019

STRUCTURAL ANATOMICAL ASPECTS OF TWO EUPHORBIA (EUPHORBIACEAE JUSS.) SPECIES LEAVES

DAN RĂZVAN POPOVICIU, RODICA BERCU Faculty of Natural and Agricultural Sciences,”Ovidius” University, Constantza University Alley, No. 1, B, 900470, Constantza E-mail: [email protected]

Abstract. The paper presents a study concerning the leaf structure (petiole, as the case) and blade of two Euphorbia species belonging to Euphorbiaceae family: Euphorbia trigona Mill., and E. tirucallli L. In literature is little information concerning the leaf petiole or blade anatomy of species of Euphorbia genus in general and concerning these two species in particular. The petiole of Euphorbia trigona possesses one epidermis cells which are more or less rounded in shape, covered by a thin cuticle. The vascular system of the petiole is represented by three closed–collateral vascular bundles. Anatomically, the leaves blade of the studied species are heterogenous and amphistomatic with lacticifers especially presented to the midrib zone, more abundant în Euphorbia tirucalli. The midrib vascular system is more developed in Euphorbia tirucalli than E. trigona.

Keywords: anatomy, leaf, mesophyll, laticifers, Euphorbia

INTRODUCTION a bushy harvested port, with the The studied species belong to appearance of green rods and thick Euphorbiaceae family, one of the branches as a pencil (hence the largest in the plant world, sometimes popular name of the plant). Leaves are known as spurges. It includes around rare and small (Fig. 1, A). It develops 300 genera and 7,700 species, mainly well in hydroculture’s (Burger and Huft, non-succulent herbs, shrubs and trees 1995). It is a very toxic euphoric found in temperate, sub-tropical and species, currently used more as an tropical climates. The spurge family ornamental plant (Miaulane, 2004). takes its name from the genus Euphorbia trigona Mill. is a Euphorbia. Euphorbia tirucalli L. perennial plant, originating from (pencil plant, milky shrub, pencil cake) Central Africa, with more popular is a perennial plant native from Africa names as the African milk tree, cactus where it was very widespread. cathedral (Broschat and Meerow, Currently, it can also be found 1991; Fuller and McClintock, 1986) or spontaneously, in restricted areas, in cactus -candle (Miaulane, 2004), the center, southern and northeast of The plant has a straight, thick the African continent. It is a plant stem, 3-4 lined, slightly branched, dark included in the IUCN Red List of green with lighter green and V-shaped Species since 2006 and has been pattern. threatened with extinction since 2004 On the stem crest the thorns are (Haevermans, 2004). It is a plant with tall, twisted, about 5 mm in length.

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Among stems and spines are rare, general studies concerning the oblong-lanceolate leaves, with the angiosperms anatomy (G. Bonnier and whole margin, which appear in the Leclerc du Sablon, 1905; Dilcher, spring, placed especially in the top of 1974; Esau, 1965; Metcalfe and Chalk, the stems (Fig. 1, B). In our country it 1950; Napp-Zinn, 1973, 1974). is known as an ornamental plant. The Romanian literature there In literature is little information are only a few data on the structure of concerning the leaf anatomy of species some vegetative organs (Ivanescu and of Euphorbia genus in general and Toma, 2003) of Euphorbia species; or concerning these two species in general mentions in some lectures particular. articles and manuals of Anatomy and Mostly researches followed the Morphology of Plants (Bavaru and origin, development and structure of Bercu, 2002; Galeş and Toma, 2007; the laticifers. The most ample paper Grințescu, 1985, Niculescu, 2009; which analyzes the structure of the Șerbănescu-Jitariu and Toma, 1980; stem and leaf of spontaneous species Toma and Gostin, 2000;). and not only, from the Euphorbiaceae The purpose of this paper is to family is that of Gaucher (1902). highlight the anatomical characteritics Succinct references on the structure of of those two species. This paper could the leaf as vegetative organ of some bring more information about this Euphorbia species are found in some genus and this large family.

A B Fig. 1. Euphorbia tirucalli L. (A). Euphorbia trigona Mill. (B) (original).

MATERIAL AND METHODS Small pieces of mature leaves The mature leaves, of were fixed in FAA (formalin: glacier Euphorbia tirucalli and E. trigona were acetic acid: alcohol 5:5:90). Cross collected from S.C. IRIS S.R.L. sections of the vegetative organs were Greenhouse and from the Vegetal performed by manual technique used Morphology laboratory of the faculty. in vegetal histology (Bercu and Jianu 157

2003). The samples were stained with RESULTS AND DISCUSSION alum-carmine and iodine green. The petiole is present only at Anatomical observations and Euphorbia trigona leaf. In cross- micrographs were performed with a section, the petiole has a triangular BIOROM–T bright field microscope, contour shaped determinate by the equipped with a TOPICA 6001A video presence of two developed lateral camera. wings (Fig. 2).

Fig. 2. Cross section of Euphorbia trigona petiole: bs- basic tissue, co- collenchyma, e- epidermis vb- vascular bundles.

The epidermis cells are more or The blade. The blade epidermis less rounded in shape, especially in of Euphorbia tirucalli is one-layered the vascular bundles area, slightly celled and exhibits to upper and lower cutinized and covered by a thin cuticle. epidermis slightly rounded contour, Beneath the epidermis is a covered with a thin cuticle. The lower hypoderm, represented by a epidermis forms a slightly vault. At this collenchyma tissue with chloroplasts species, notable are the lateral parts of (3-4 layers of cells) with mechanical the blade that have a sinuous outline, role (Fig. 2). with the margins slightly curved Centrally located, in a basic towards the adaxial face (Fig, 3). parenchyma, is the vascular system of Among the lower and upper epidermis the petiole, represented by 3 closed – cells, rare stomata are present (Fig. 4, collateral type vascular bundles A).

Fig. 3. Cross section of the mesophyll of Euphorbia tirucalli – ensemble: le- lower epidermis, ms- mesophyll, ue- upper epidermis, vb- vascular bundle of the midrib zone.

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heterogeneous and amphistomatic Cross sections of the blade with laticifers (Fig. 4, A). exhibits an upper and lower The main vain is represented by epidermises, both one-layered and the a collateral bundle (Raven et al., 1992) mesophyll with vascular bundles formed by xylem and phloem embedded. The mesophyll is elements. Laticifers are present as well (Fig. 4, B).

A B

Fig. 4. Cross sections of Euphorbia tirucalli blade. Portion with mesophyll (A) Portion with midrib zone (B): co- collenchyma, l –lactiferous tube, ph- phloem, pt- palisade tissue, s- stomata, sc- sub-stomata cavity, sp- spongy tissue, ue- upper epidermis, x- xylem.

The sessile leaf of Euphorbia between the palisade tissue layers and trigona has one layered upper and lower epidermis. The mesophyll is lower epidermis, covered by a thin amphistomatic with lacticifers cuticle, followed by a heterogeneous especially presented to the midrib zone mesophyll with 2 layers of palisade (Fig. 5, 6, A). The main vain is tissue just below the upper epidermis represented of a collateral bundle with and a number of spongy tissue xylem and phloem elements.

Fig. 5. Cross section of Euphorbia trigona blade - ensemble: co- collenchyma, le- lower epidermis, ms- mesophyll, ue- upper epidermis, vb- vascular bundle.

As Batanouny (1992) reported findings are the same for Euphorbia for other Euphorbia species, our trigona concerning xylem conductive 159

elements which are placed towards the elements, placed towards the lower upper epidermis and exhibits a more or epidermis, are poor developed than less radial arrangement. Phloem xylem ones (Fig, 6, B).

Fig. 6. Cross sections of Euphorbia trigona blade. Portion with mesophyll (A). Portion with midrib zone (B): l- laticifer tube, Ale - lower epidermis, ms- mesophyll, ph- phloem, ptB- palisade tissue, sp- spongy tissue, x- xylem.

Just like in other studied less thin cuticle. The continuity of both Euphorbia sp. (Galeş and Toma, 2007) epidermises is broken by the presence in the mesophyll of these two species, of stomata, more abundant in the lower especially in the spongy tissue, the no epidermis. The mesophyll of both articulated laticifers are present around species is heterogeneous and the phloem tissue and have cellulosic amphistomatic with lacticifers thin walls, round or polygonal shape. In especially presented to the midrib all studied species laticifers are also zone. The midrib vascular bundle of present mainly in the phloem aria of both species possesses xylem the vascular bundles (Fig. 4, A, B: 6, elements to the upper epidermis and B). phloem elements, placed towards the CONCLUSIONS lower epidermis which are poor The petiole of Euphorbia trigona developed than xylem one. The possesses epidermis cells which are secretory elements – laticifers - are more or less rounded in shape, slightly placed mainly in the main vein aria, but cutinized and covered by a thin cuticle. also in the mesophyll, in all studied The vascular system of the petiole, species.The mechanical tissue is not represented by three closed –collateral very well represented. It occurs such type vascular bundles. Cross sections as collenchyma tisuue in Euphorbia of the leaf blade of the two studied trigona petiole and to the lower species (Euphorbia trigona și E. epidermis for the blade of this species. tirucalli) exhibits a single layered upper It is poor developed for Euphorbia and lower epidermis which differ in tirucalli leaf blade. shape and size, covered by a more or

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