ACTA AGROBOTANICA Vol. 65 (2): 23–36 2012 FLORAL PHENOLOGY, FLORAL REWARDS AND INSECT VISITATION IN AN ORNAMENTAL SPECIES Geranium platypetalum Fisch. & C. A. Mey., GERANIACEAE Marzena Masierowska University of Life Sciences in Lublin, Department of Botany, Akademicka 15, 20-950 Lublin, Poland e-mail: [email protected] Received: 03.01.2012 Abstract and Lande, 2009). A quantitative characterization of This 4-year study examined the flowering pattern, floral flowering phenology is possible by examining the flo- display, nectar and pollen production as well as insect visitation wering distribution curve, i.e. the number of open flo- to a perennial Geranium platypetalum Fisch. & C. A. Mey. wers per census day for the whole flowering duration G. platypetalum bloomed from the end of May until the (Rathcke and Lacey, 1985). In plants that display end of June. The pattern of flowering shows the skewed distri- multiple flowers simultaneously, the floral display, ra- bution with a tendency towards a more symmetrical curve. The ther than the individual flower, is the basic unit of plant flower display size fluctuated during the flowering season. The mating. Plants with large floral displays usually attract most intense blooming fell in the 2nd and 3rd flowering week. more pollinators than those that have small displays, The flowers exhibit incomplete protandry. and pollinators tend to visit more flowers on large dis- Nectar productivity differed significantly between plays (reviewed by Ohashi and Yahara, 2001; and stage of flower development. Ten and flowers se- Kudo and Harder, 2005). creted 29.8 mg and 17.6 mg of nectar, on average, respectively, with mean sugar content of 33.9% and 43.1%. The mean total The flowering pattern of a species is of a gre- sugar mass in nectar was similar for both stages and the values at importance when the insect-plant relationships are were 10.2 mg and 8.2 mg, respectively. Pollen mass per 10 flo- investigated, especially if the taxon is considered as wers was 19.06 mg. a food source for visitors. The Geranium species are Bees (Apoidea) were the principal visitors on Geranium among plants which can supply insects with ample flowers. The peak of daily activity of visitors occurred between nectar and pollen food. 10.00 and 14.00 hrs. The insects gathered mainly nectar. The The genus Geranium L. (Geraniaceae), crane’s mean visiting rate was 0.149 visit per flower×min-1. bill, comprises approximately 400 species distributed Increased use of G. platypetalum in parks and gardens in temperate areas and tropical mountains throughout is recommended in order to enrich the nectar pasture for A. mel- most of the world (Zomfler, 1994; Aedo et al. lifera and wild Apoidea. 2007). According to Rutkowski (1998) 21 Gera- nium species occur in Polish flora. Some species are Key words: Geranium platypetalum, flowering pattern, nectar, used as medicinal plants with antioxidant properties pollen, protandry, bees due to a high flavonoid and tannin content (M i ł - kowska et al. 1998; Ghimire et al. 2006; A n - tal, 2010). They also provide essential oils (mainly INTRODUCTION geranium oil) for cosmetic purposes. Numerous crane- Variations in flowering phenology represent ’s bill species and cultivars are widely grown as orna- adaptation to various modes of pollination and are as- mentals, especially in naturalistic parks and gardens. sociated with the reproductive systems (reviewed in Their decorative value derives from beautiful and Goodwille et al. 2010). Changes in flowering time abundant flowers as well as from dense leaf canopies allow plants to synchronize reproduction with conspe- covering the ground. These plants are very easy in cul- cifics and pollinators, and to reduce competition for tivation and perform well both in full sun and in shade pollination (Waser and Real, 1979; Devaux conditions. 24 Marzena Masierowska Geranium flowers appear to be typically ento- MATERIALS AND METHODS mophilous because of their visually attractive petals, robust stigmas, abundant pollen and the presence of ac- Study site and plant species tive nectaries. Moreover, these actinomorphic flowers The present study was conducted on a cultiva- produce conspicuous nectar guides, generally similar ted plot of G. platypetalum grown on a loess-origin on all petals (Link, 1990). Wild crane’s bills are eager- soil in the Botanical Garden of Maria Skłodowska-Cu- ly visited by insects attracted mainly by nectar with rie University, Lublin, Poland (N-51o09’, E -22o27’). a high sugar content. The census plot occupied an area of 7 m2. The obse- Among taxa occurring in natural habitats, the rved plants grew in a dense patch so it was difficult to best known, valuable nectariferous plants are Gera- discriminate the individuals and to count their number. nium pratense L. (Larsson and Shuel, 1982; Geranium platypetalum Fisch. & C. A. Mey., Jabł o ń ski, 1998; Lipiń ski, 2010) and G. syl- synonymous with G. ibericum var. platypetalum vaticum L. (J a b ł o ń ski and K o ł towski, 2002). (Fisch. & C. A. Mey.) Boiss., is a perennial herb, Also, G. collinum Steph. (M i ń kov, 1974), G. pheum 25-57 cm tall, which is native to northeast Turkey, L. (Mountain et al. 1981) and G. sanguineum L. Caucasus, and northern Iran and cultivated since 1802. (Masierowska, 2006) are listed among good The stem is erect, leafy, herbaceous. Basal leaves in a melliferous species. Moreover, the presence of Gera- rosette. Rootstock ± horizontal. The flowers are her- nium pollen was stated in pollen loads of honey bees maphroditic, actinomorphic, disc-shaped, 3-4.5 cm (Hodges, 1952; Szwan and Martinovs, in diameter, deep blue with red veins, clustered in 1954) and bumblebees (Teper, 2002). Hymenopte- a dichasial cyme with 2-flowered cymules. The se- ra are the main insect visitors on flowers of different xual parts, consisting of a pistil and surrounding Geranium species (Proctor et al. 1996; Kando- 10 stamens, stand straight in the center of flower. An- r i , 2002; Kozuharova, 2002; Masierowska, thers are blue-black and gynoecium is dark purplish. 2006). Phenology and abundance of flowering In the recent literature there are very scarce The study on phenology of flowering was car- data on plant-insect relationships in cultivated crane’s ried out on the species level as well as flower level bills (J a b ł o ń ski and K o ł towski, 2002; M a - (Dafni, 1992). During the period 2009-2011 flowe- sierowska, 2006). Ornamental species and culti- ring onset and flowering termination were recorded to vars planted in urban regions may help sustain local determine the timing and duration of flowering. Mo- pollinator populations as well as broaden food sour- reover, in the years 2009-2010 the dynamics of flo- ce for maintained insects such as honey bees or some wering per area unit was examined as well. For this species of solitary bees and bumblebees (Denisow, purpose, prior to opening of the first flowers, 5 plots, 2008). These natural pollinators are of potential value each 50×50 cm in size were selected at random on the in open and closed crop production systems and their patch and marked. On each plot, daily or every second population size should be increased by, among others, day, all new flowers that opened were counted and ensuring their refuges and nesting places as well as ful- marked with a marker until blooming terminated. The filling food resource requirements (Goulson, 2003; values were recalculated per 1 m2 area. The dynamics Klein et al. 2007; Williams and Kremen, of flowering was expressed as the percentage of newly 2007). The habitat’s heterogeneity promotes biodiver- opened flowers on successive flowering days in rela- sity in human landscapes and hence may provide ‘bio- tion to the total number of flowers eventually formed logical insurance’ for services currently rendered by on the plot (100%). The total number of flowers was managed insect species (Ives et al. 2000; Winfree determined per 1 m2 area as well as per inflorescence. et al. 2007). Moreover, the development stages of G. platypetalum The aim of present study was: (1) to examine flowers were observed. Floral persistence was counted floral phenology in one of most showy ornamental as the days from the opening to the falling of all petals. species Geranium platypetalum, (2) to investigate The length of flowering of a single inflorescence was floral rewards available to visiting insects and (3) determined, too. to monitor the activity and spectrum of insects col- lecting these rewards. The primary purpose of this Floral reward measure investigation was to determine the floral traits in G. Preliminary observations on localization of flo- platypetalum beneficial for relationships with visiting ral nectaries were conducted. After removing elements insects as well as to check if these plants can supply of the corolla and anthers, the whole glands from fresh their flower visitors with an ample, high quality food material were examined under a stereoscopic micro- during spring time, i.g. the period of high food de- scope. Nectar productivity was examined in the years mand by bees. 2007, 2009-2010. To determine it, flower buds were Floral phenology, floral rewards and insect visitation in an ornamental species Geranium platypetalum Fisch. & C. A. Mey... 25 isolated in the field and nectar was collected from per- flower×min-1). Observation discriminated four insect fect flowers at two different stages of flower develop- categories: honey bees, bumblebees, solitary bees, ment: male stage ( )-flowers with full pollen presen- others (flies, ants). Relative abundance and daily visi- tation (Fig. 1), and the female stage ( )-flowers after tation pattern of these categories were determined. pollen exposure with fully expanded stigmas (Fig. 2). Data analysis The nectar was gathered using glass micropippets and its amount was measured (in mg).