Abstract
Epipogium aphyllum is a European-Asian obligatory mycoheterotrophic orchid containing no chlorophyll. Flowers are not resupinate with a sack-shape spur and cordate lip, which is divided into two parts: the basal (hypochile) and distal one (epichile). The floral analysis provides strong evidence to conclude that nectar is secreted on the upper surface of pink-coloured papillate ridges and epidermal (adaxial) cells at different place in spur, especially at the apex. The exudation on papillae has been observed through the entire anthesis and it has been stained on polysaccharides, proteins, and lipids. The dense cytoplasm of papillae contains profuse endoplasmic reticulum, plentiful vesicles (bigger ones with tannin-like materials), numerous mitochondria, sometimes dictyosomes, starch grains, and plastids with tubular structures. The large electron-dense bodies in cell walls are structurally the same as tannin-like materials from vesicles that are in contact with plasmalemma. The rupture of thin layer of swelled cuticle is caused by pressure of gathered substances exuded due to granulocrine secretion. The idioblasts with raphides occur mainly in tepals tissue. The dynamic changes of the nectar exudation, released through endocrine secretion, have been noticeable during the anthesis: both on the lip and inside the spur. The nectar secretion is not dependent on the colour form of E. aphyllum blooming shoots. The floral biology and ultrastructure differ from mycoheterotrophic plants known up to date.
Highlights
The nectar secretion and scent production in orchid flowers can be divided into three groups
Floral material for the study was collected from the largest population of Epipogium aphyllum in Poland, which is located in Darzlubska Forest, near Wejherowo, in the Pobrzeze Kaszubskie region [9]
Three forms of blooming shoots according to different pigments were distinguished in the Darzlubska Forest population (Figure 1(a))
Summary
The nectar secretion and scent production in orchid flowers can be divided into three groups. The species from the first one, for example, Anacamptis, Gymnadenia, and Platanthera, produce the nectar and emit a strong scent. For example, Dactylorhiza and Orchis, emit delicate scent, but do not produce nectar and their floral appearance often mimics nectariferous plants [1]. The investigated orchid species, Epipogium aphyllum (Ghost Orchid), is a very rare, terrestrial obligatory mycoheterotrophic orchid containing no chlorophyll It is known for its intermittent (like a “ghost”) appearance. It belongs to the first group: it produces nectar and emits scent, most frequently defined as the vanilla fragrance [2,3,4] and sometimes as the banana one [1, 2].
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