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  • Subject area(s): Science
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  • Published on: 15th October 2019
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In all Ophrys species, the labellum has adapted to draw the attention of passing insects, through distinctive shapes, colours, scents and textures. O. apifera attracts male bees through the use of mimicry in the hope that they will try to mate with the flower and in doing so, will aid pollination (Kew Science, 2018). The labellum is convex and three-lobed; the two lateral lobes forming furry brown humps, while the middle lobe, velvety in texture with brown stripes outlined in yellow, forms the rounded body of the “bee”, (Mokni et al., 2013).

Review of basic biology:

Ophrys apifera is a perennial orchid with many flowers, each of which has three petal-like outer tepals, two inner tepals that resemble antennae and a large lip mimicking a bee (Kew Science, 2018). O. apifera are monocarpic, which explains their irregular appearance with large numbers some years and absence in others. O. apifera self-pollinates; the pollinia hang below the anther and are blown against the surface of the stigma (Osiadacz and Kręciała, 2014). Pollination in O. apifera can be achieved in two ways – with the participation of males of Eucera or autogamically (Kullenberg and Berg-ström, 2008, as cited in Osiadacz and Kręciała, 2014).

Anatomy:

An O.apifera plant has two ovate tubers and the stems can reach up to 50cm tall (Soó, 1980, as cited in Osiadacz and Kręciała, 2014). The different Ophrys species vary, however, their basic structure and function are alike, for example, the anther is always situated above the stigma. Anther cells contain a pollinarium, consisting of pollinium (the pollen mass), a caudicle and a viscidium. Each viscidium is enclosed in a separate bursicle. The caudicles are curved forward and are rigid enough to stand upright in the anther cells, awaiting the insects which will transport them to another flower. Its gynostemium is easily recognisable by its distinct S-shaped, as shown in Figure 2 (Classens and Kleynen, 2002). Most O.apifera plants typically have two to three flowers, however, some individuals can reach up to ten flowers. Each of which has a lip resembling a bee, and three large pink or white, petal-like outer tepals and two inner tepals ranging from 12-16mm long. After the flowers open, the caudicles dry and shrink, exposing the pollinia so that they hang downwards under their own weight and land onto the stigma, as shown in Figure 1 (Mokni et al., 2013).

Ecology:

O. apifera is a Euro-Mediterranean species which typically inhabits dry, open grassy slopes often on chalk or limestone soil (Kew Science, 2018). The species typically grows in small groups of 1-3 individuals. It is one of the most successful Ophrys species as proven by its vast area of distribution (Soliva et al., 2001, as cited in Classens and Kleynen, 2002). It is widely spread across Europe (as shown in Figure 3), spanning from western Europe, northwards to Northern Ireland, east to the Caucasus Mts. and southwards to North Africa (Soó, 1980, as cited in Mokni et al., 2013). It is a pioneer species and among the first to appear on disturbed sites (Wells and Cox, 1991 as cited in Osiadacz and Kręciała, 2014). Seed germination occurs in March and the minute seeds are produced in thousands and can be distributed several kilometres. This explains the unexpected appearance of O.apifera in urban locations and exposed ground such as on road-cuttings, quarries and other industrial sites (Mokni et al., 2013).

Scientific Importance:

O. apifera, in contrast to most other Ophrys species, is autogamous. However, there is disagreement about the self-pollination process itself. Some researchers suggest that the pollinia, after leaving the anther, hang freely in the air and rely on an external factor such as wind to make contact with the stigma. On the other hand, others believe that external factors alone are not sufficient enough to make contact between the stigma and pollinium and that it requires a mechanical physiological process.

Observations by Classens and Kleynen (2002) suggest that the pollinia hang freely in front of the stigma and that wind is essential in the pollination process. A gust of wind is enough to make the pollinia, that have left the anther, swing and eventually making contact with the stigma, after which auto-pollination takes place. Findings from Kullenberg (1961) also reflects this after finding that the pollinia, if placed in a wind-free environment, stay immobile once descended from their anther, demonstrating that external influences form an essential part of the pollination strategy of O. apifera (Classens and Kleynen, 2002). The pollinaria, and more specifically the caudicles, play an important role in the process of auto-pollination. Kullenberg (1961) found that each caudicle has a slender, basal part and a longer sturdier part, connected to the pollinium, as shown in Figure 2 (Classens and Kleynen, 2002). According to Kullenberg (1961), a triangular thickening is formed at about a third of the length of the caudicle. This creates mechanisms similar to that of a joint, which enables the caudicles to bend and enables movements of the pollinarium in all directions. Furthermore, Classens and Kleynen (2002) found that the caudicles are not solid, but instead contain hollow spaces, weakening their structure. This enables them to bend forward, further facilitating autogamy.

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