ACTA AGROBOTANICA Vol. 62 (2): 13–21 2009

THE POSITION AND STRUCTURE OF THE NECTARY IN SPRING HEATH ( carnea L.)

Elżbieta Weryszko-Chmielewska1, Mirosława Chwil1, Marek Wróbel2

1Department of Botany, University of Life Sciences in Lublin, 20-950 Lublin, Akademicka 15, Poland, e-mail: [email protected] 2Central Apparatus Laboratory, University of Life Sciences in Lublin, B. Dobrzańskiego 3, 20-290 Lublin, Poland

Received: 7.07.2009

Abstract which contains numerous tiny seeds (H egi, 1959; Ecological traits of Erica carnea L. flowers and the Szweykowscy, 2003; Czekalski, 2008). morphology of floral nectaries were investigated using stereosco- Erica carnea L. has flowers with pink, light car- pic, light and scanning electron microscopy. The nectary in the mine or white corollas forming short hanging . flowers of Erica carnea is located in the basal part of the ova- It flowers from March to May. Evergreen are ry. It represents the gynoecial nectary type. It has the of 8 mm long; they are needle-like, dark green and are a yellow, ribbed ring with eight outgrowths, pointed towards the borne in whorls of four. Erica carnea L. is native to the base, which alternately adjoin the stamen filaments. The height mountainous areas of South and Central Europe. This of the nectary is 400 μm and its thickness 200 – 250 μm. The is a very frequently grown in gardens. Represent- parenchyma of the nectary is composed of 6 – 8 layers. Nectar atives of this are clumped shrublets, reaching secretion occurs through anomocytic stomata with a diameter of a height of 20 – 50 cm (Podbielkowski and S u d - 17 μm. Guard cells are only found on the outgrowths of the ne- nik-Wójcikowska, 2003; Szweykowscy, ctary and they are situated most frequently at the level of other 2003; C h ojnowscy, 2008). epidermal cells. During nectar secretion, a small degree of pore opening was observed. In the flowers of Erica carnea, seconda- According to S mets (1986), the floral nectar- ry nectar presentation was found, with the nectar accumulating ies found in form a disc covering the nec- at the base of the fused corolla. tary surface and they are included in nectaria persis- tentia. Maurizio and Grafl (1969) describe the Key words: Erica carnea, floral nectary, position, size, micro- nectaries of Erica as a ring, which has 8 outgrowths morphology pointed downwards, surrounding the superior ovary. On the other hand, Bernardello (2007) defines the nectaria in Ericaceae as intrastaminal. The nectar- INTRODUCTION ies located on the surface of the basal part of the ovary are also found in other representatives of Ericaceae, In the Ericaceae family, different struc- belonging to the genus Rhododendron (Werysz- tures are found. These flowers differ from one another ko-Chmielewska and Chwil, 2005, 2007; in their symmetry, the number of elements in particular Weryszko-Chmielewska et al. 2003, whorls (4 or 5) and the position of the ovary in the 2007; Chwil and Weryszko-Chmielew- flower (inferior or superior). The position and structure ska, 2009). of the nectary are related to the structure of the pistil in The aim of the present study was to determine this family (B e rnardello, 2007). the size and micromorphology of floral nectaries of Heath (Erica) flowers are bisexual, 4 – petalled, Erica carnea L., the structure of which has not been with colourful corollas. They occur in small racemose examined sufficiently to date. inflorescences at the stem tips. The corolla is gamo- petalous, bell- or cup-shaped. Two whorls are distin- MATERIALS AND METHODS guished in the androecium composed of 8 stamens. The pistil with superior ovary has a long style. The perianth The study of flowers of Erica carnea L. = Erica persists in petal-shedding flowers, where it dries up herbacea L. was conducted in the years 2007-2008, in and surrounds the forming fruit. The fruit is a capsule the Botanical Garden of the Maria Curie-Skłodowska 14 Elżbieta Weryszko-Chmielewska, Mirosława Chwil, Marek Wróbel

University in Lublin. Flowers were sampled at the full The stomata are only located on the surface of the bloom stage of the studied shrublets. Ecological traits hook-like outgrowths (Figs 3A, B), whereas the remain- of flowers and the morphology of floral nectaries were ing part of the nectary epidermis is devoid of stomata. determined using stereoscopic, light and scanning elec- They occur most frequently at the level of the other epi- tron microscopy (SEM). dermal cells (Figs 3C, D). Only some of them are situat- Under a light microscope in cross section, the ed on small protuberances (Figs 4A, D). The stomata are nectariferous tissues were analysed and the number of formed singly or in twos next to each other (Figs 3B, D). nectar-secreting cells was determined. The height and When viewed from above, they have a circular shape (a diameter of the ovary and nectary were measured, as 17 μm diameter) and they are surrounded by 7 – 8 epi- well as the distance between the hook-like outgrowths dermal cells. They are included in the anomocytic type. of the nectariferous tissue. The position and type of the The surface of the epidermis is covered by a smooth cu- floral nectary were determined. ticle layer. The cuticle forming fine striae is only found The plant samples used for SEM observation of on the walls of the guard cells. the structure of the epidermis covering the nectary were Parenchyma cells of the nectary were composed fixed in buffered glutaraldehyde. After dehydrating in of 6 – 8 layers. The colour of the nectary results from acetone and critical-point drying in liquid CO2, they the presence of chromoplasts in their protoplasts. were coated with gold using a Sputter Coater. Under During nectar secretion, a small degree of pore a scanning electron microscope TESLA BS-300, the opening was observed in most of the stomata of the following traits were analysed: the shape of cells of the nectary epidermis (Figs 3A – D). Small outer cuticular nectariferous epidermis and cuticular ornamentation as ledges occur around the pores. In the slides viewed un- well as the topography and type of stomata. der a scanning electron microscope, traces of dried se- cretion were observed on the surface of the stomata or RESULTS in their vicinity (Figs 3B, D). The nectar flowing from the downward-pointed outgrowths of the nectary (Fig. Flower morphology 4D) accumulated in the lower part of the corolla tube, The attractiveness of Erica carnea flowers is from where it was collected by insects. Therefore, it determined by their pink corolla petals and dark purple can be stated that secondary nectar presentation occurs anthers protruding beyond the ampoule-shaped corolla in this species. (Figs 1A, B). Xeromorphic features occurring in Erica carnea are manifested not only in its structure, but DISCUSSION also in flower morphology. Both sepals and petals are slightly leathery and they persist for a long time on In the present paper, the micromorphology of the plant. The corolla is 4 – 5 mm long and it is twice the nectary of Erica carnea is presented for the first longer than the sepals (Fig. 1B). time. Due to its position in the flower, it is included The lower parts of the long stamen filaments ad- in gynoecial nectaries associated with the base of the join the depressions in the basal part of the cylindrical ovary. This nectary has the form of a ribbed ring with ovary of the pistil, in which the nectary gland is located outgrowths pointed towards the pedicle. The position (Figs 1C, D). The nectary is distinguished by its or- of the nectary on the ovary surface shows that the defi- ange-yellow colour and it has the form of a ribbed ring nition of Smets (1986) as well as of Maurizio with hook-like outgrowths. The stamen filaments are and Grafl (1969), who describe it as a disc covering arranged alternately relative to the protrusions of the the ovary base, is right with regard to the nectary found nectary (Figs 1C – E, G). Nectar secretion occurs in the in Erica flowers. But the definition of B ernardello basal part of the nectary (Fig. 1F). (2007), who finds that the intrastaminal receptacular nectary occurs in Ericaceae, does not seem to be ap- Nectary micromorphology propriate with respect to this genus. The floral nectary of Erica carnea L. forms a pro- Anderson et al. (2000) showed that in Per- 1 nettya rigida (Ericaceae) the nectary formed 10 out- trusion covering about /4 of the height of the nectary (Figs 2A – D). Eight ribs terminating in hook-like outgrowths growths located between the superior ovary and the at the bottom can be distinguished in it (Figs 1E, D, 2A corolla. These outgrowths occurred alternately with – D). These outgrowths are arranged alternately with the the stamen filaments. stamens adjoining the depressed parts of the nectary. The Freitas et al. (2006) described nectaries in height of the ovary in Erica carnea is 1.6 – 1.7 mm, and other Ericaceae representatives. In several Gaultheria the diameter in the region where the nectary occurs is 0.9 species, interstaminal nectaries occurred. They ob- – 1 mm. The nectary ring is about 400 μm in height, and served a ten – segmented nectary around the ovary base its thickness reaches 200 – 250 μm (Tab. 1). in Agarista. The nectary gland in the form of a ring The position and structure of the nectary in spring heath (Erica carnea L.) flowers 15

Table 1 Characteristics of the ovary and nectary in Erica carnea flowers.

Investigated trait

length 1.6 – 1.7

Ovary at half-length mm 0.80 – 0.85 diameter in the part with the nectary 0.95 – 1.00

height 400

min – max 230 – 290 by the protrusions average 250 thickness of the μm nectariferous tissue min – max 190 – 211 in the depressions average 200

number of hook-like outgrowths 8

min - max 131 –190 Nectary distance between outgrowths μm average 165

number of the nectary’s parenchyma layers 6 –8

diameter min – max 15 – 19 μm average 16.8

number on the surface of an outgrowth 8 – 10 stomata type anomocytic

apical region of position hook–like outgrowths

at the ovary base with distinct ribbing has been fo- In the epidermis of the Erica carnea nectary, und in several Rhododendron species (W eryszko- most of the stomata were located at the level of other Chmielewska and Chwil, 2005, 2007; W e - epidermal cells. But in of the genus Rhododen- ryszko-Chmielewska et al. 2007; Chwil dron, we have shown that these stomata are often el- and Weryszko-Chmielewska, 2009). evated above the surface of the nectary (W erysz- Our study showed that nectar secretion in Erica ko-Chmielewska and Chwil, 2005; 2007). carnea occurred through few stomata which were only Similarly like in Erica carnea, we have observed located in the basal part of the nectary in the region anomocytic stomata in the nectaries of Rhododendron of the hook-like outgrowths. But in the nectaries of (Weryszko-Chmielewska et al. 2007). several species of the genus Rhododendron, the occur- The nectary of Erica carnea is yellow-col- rence of stomata was found on the whole surface of the oured, which results from the presence of chromo- nectary. They were located singly or in different clus- plasts. Chromoplasts in parenchyma cells of the nec- ters (W eryszko-Chmielewska and Chwil, tary have been also observed in species from other 2005, 2007; Weryszko-Chmielewska et botanical families, among others in Chamaelaucium al. 2007). On the other hand, no stomata at all were uncinatum (O’Brein, 1996) and Nicotiana tabacum found in the epidermis of the floral nectary of Parnet- (Thonburg, 2007). tya (Anderson et al. 2000). The authors think that in this case nectar must be exuded through the rugged cuticle of the nectary. 16 Elżbieta Weryszko-Chmielewska, Mirosława Chwil, Marek Wróbel

Fig. 1. Erica carnea flowers and their portions. A – Portion of an inflorescence, x 7. B – Flower with bracts (l) , x 13. C – Generative elements of a flower after exposing the corolla; between the lower portions of the filaments, protrusions of the nectary are visible (arrows), x 16. D – Pistil with a green ovary and yellow nectary (arrow) at the ovary base, x 16. E – Lower part of the ovary with the nectary (n), x 512. F – Outgrowths of the nectary viewed from the side of the pedicle, x 230. G – Nectar droplet on the nectary surface, x 390. The position and structure of the nectary in spring heath (Erica carnea L.) flowers 17

Table 2 Comparison of nectary morphology in several plant species of the family Ericaceae.

Nectary Stomata Nectar Autor Species exuded type located type distributed through

Agarista hispidula 10 segmented around the Freitas et al. inter–staminal –– ovary base (2006) A. oleifolia

a ribbed ring at the base singly or in Results in the Erica carnea gynoecial anomocytic stomata part of the ovary twos present paper

Gaultheria projections around the – sleumeriana ovary base Freitas et al. inter–staminal (2006) Gaylussacia around the style over the – chamissonis ovary

10 outgrowths occurred alternately with the through Pernettya Anderson et al. receptacular stamen filaments, – the rugged rigida (2000) between the superior cuticle ovary and the corolla

Weryszko-Chmie- Rhododendron at the base of the ovary, singly quite gynoecial anomocytic stomata lewska et al. catawbiense ribbing nectary evenly (2007)

actinocytic; singly Weryszko–Chmie- compact R. japonicum gynoecial at the base of the ovary and stomata stomata lewska and Chwil stomata fields (2007) fields

Weryszko-Chmie- a bulge at the basal part of singly and R. luteum gynoecial anomocytic stomata lewska and Chwil the ovary evenly (2005)

CONCLUSIONS 2. Nectar secretion occurs through the stomata situ- ated only in the apical parts of the outgrowths of the 1. The nectary in the flowers of Erica carnea is lo- nectary. cated in the basal part of the ovary and it represents the gynoecial nectary type. 18 Elżbieta Weryszko-Chmielewska, Mirosława Chwil, Marek Wróbel

Fig. 2. Erica carnea ovary with the nectary (SEM). A – Elongated ovary with the nectary (n) at the base, bar = 500 μm. B – Nectary (n) forming a ring-like protrusion on the ovary, bar = 200 μm. C – Hook-like outgrowths of the nectary (asterisks) viewed from the side of the pedicle, bar = 200 μm. D – Basal part of the nectary with outgrowths, bar = 90 μm. The position and structure of the nectary in spring heath (Erica carnea L.) flowers 19

Fig. 3. Portions of the surface of the Erica carnea nectary (SEM). A, B – Isodiametrical epidermal cells and stomata in the apical region of the hook–like outgrowths, A – bar = 60 μm, B – bar = 30 μm. A, B, D – Visible traces of dried secretion C, D – Anomocytic stomata of the nectary, bars = 20 μm. 20 Elżbieta Weryszko-Chmielewska, Mirosława Chwil, Marek Wróbel

Fig. 4. Stomata and nectar on the surface of the Erica carnea nectary (LM). A – Stoma located at the level of other epidermal cells, bar = 30 μm. B – Stoma situated on a small protuberance, bar = 20 μm. C, D – Nectar droplets flowing out of stomata, bars = 20 μm.

REFERENCES Maurizio A., Graf l I., 1969. Das Trachtplanzenbuch. Ehrenwirth Verlag, München. Anderson G. J., 2000. Dioecy and wind pollination in Per- O ’ B r i e n S. P., L o v e y s B. R., Grant W. J. R., 1996. Ultra- nettya rigida (Ericaceae) of the Juan Fernández Is- structure and function of floral nectaries of Chamelau- lands. Bot. J. Linnean Society, 132: 121-141. cium uncinatum (Myrtaceae). Ann. Bot. 78: 189-196. Bernardello G., 2007. A systematic survey of floral nec- Podbielkowski Z., Sudnik-Wójcikowska B., 2003. taries. [In:] Nectaries and nectar. Nicolson S. W., Nepi Słownik roślin użytkowych. Państwowe Wydawnictwo M., Pacini E. (eds). Springer, Dordrecht: 19-128. Rolnicze i Leśne, Warszawa. Chojnowscy E. M., 2008. Azalie, różaneczniki, wrzosy S m e t s E., 1986. Localization and systematic importance of i inne wrzosowate. Multico Oficyna Wydawnicza, War- the floral nectaries in the Magnoliatae (Dicotyledons). szawa. Bull. Jard. Bot. Nat. Belg. 56: 51-76. C z e k a l s k i M., 2008. Wrzosy, wrzośce i inne rośliny wrzo- Szweykowscy A. J., 2003. Słownik botaniczny. Warsza- sowate. Państwowe Wydawnictwo Rolnicze i Leśne, wa. Poznań. T h o r n b u r g R. W., 2007. Molecular biology of the Nico- Chwil M., Weryszko-Chmielewska E., 2009. Cha- tiana floral nectary. [In:] Nectaries and nectar. Nicolson racteristics of nectaries and nectar in flowers of two S. W., Nepi M., Pacini E. (eds). Springer, Dordrecht: 265- Rhododendron species. J. Apic. Sci. 53 (1): 17-27. 288. Freitas L., Galetto L., Sazima M., 2006. Pollination Weryszko-Chmielewska E., Chwil M., 2005. by hummingbirds and bees in eight syntopic species and Morphological features of the nectary and of the pollen a putative hybrid of Ericaceae in Southeastern Brazil. grains and the foraging value of the flowers of yellow Pl. Syst. Evol. 258: 49-61. azalea (Rhododendron luteum Sweet). J. Apic. Sci. 49 Hegi G., 1959. Illustrierte Flora von Mittel-Europa. Mit (2): 5-12. besonderer Berücksichtigung von Doutschland, Öster- Weryszko-Chmielewska E., Chwil M., 2007. Mic- rieich and der Schweiz. Carl Hanser, Verlag, München. romorphology of the epidermis of the floral nectary of The position and structure of the nectary in spring heath (Erica carnea L.) flowers 21

Rhododendron japonicum (A. Gray) J. V. Suringar ex carnea położony jest w bazalnej części zalążni. Pre- E. H. Wilson. Acta Agrobot. 60 (1): 45-53. zentuje typ genoecial nectary. Ma postać żółtego, że- Weryszko-Chmielewska E., Chwil M., Michoń - browanego pierścienia ze skierowanymi ku nasadzie ska M., 2007. Micromorphology of nectaries of Rho- ośmioma wyrostkami, które międzylegle przylega- dodendron catawbiense Michx. at different flower de- ją do nitek pręcików. Wysokość nektarnika wyno- velopment stages. Acta Agrobot. 60 (2): 15-22. si 400 μm, a miąższość 200 – 250 μm. Parenchyma Weryszko-Chmielewska E., Sawidis T., Matu- nektarnika tworzy 6 – 8 warstw. Sekrecja nektaru siewicz J., 2003. Przystosowania ekologiczne kwia- odbywa się przez anomocytyczne aparaty szparkowe tów różanecznika żółtego (Rhododendron luteum Sweet) o średnicy 17 μm. Komórki szparkowe występują tylko z uwzględnieniem struktury nektarnika. / Ecological na wyrostkach nektarnika i są usytuowane najczęściej adaptations of flowers of yellow azalea (Rhododendron na poziomie innych komórek epidermy. Podczas se- luteum Sweet), including the nectary structure. Ann. krecji nektaru obserwowano niewielki stopień rozchy- Univ. Mariae Curie-Skłodowska, Sect. EEE, Hortic. 13: 17-21. lenia szparek. W kwiatach Erica carnea stwierdzono wtórną prezentację nektaru, który gromadził się u na- Localization and structure of nectary sady zrośniętej korony. in spring heath (Erica carnea L.) flowers

Streszczenie Cechy ekologiczne kwiatów Erica carnea L. i morfologię nektarników kwiatowych badano przy użyciu mikroskopii: stereoskopowej, świetlnej i ska- ningowej elektronowej. Nektarnik w kwiatach Erica