3. Introduction
• Orchidaceae is a diverse and
widespread family of flowering plants with
blooms that are often colourful and often
fragrant, commonly known as the orchid
family.
• Along with the Asteraceae, they are one of the
two largest families of flowering plants, with
between 21,950 and 26,049 currently
accepted species, found in 880 genera.
7. Distribution
• The following list gives a rough overview of
their distribution:
• Oceania: 50 to 70 genera
• North America: 20 to 26 genera
• tropical America: 212 to 250 genera
• tropical Asia: 260 to 300 genera
• tropical Africa: 230 to 270 genera
• Europe and temperate Asia: 40 to 60 genera
9. Flowers
• Orchidaceae are well known for the many structural
variations in their flowers.
• Some orchids have single flowers, but most have a
racemose inflorescence, sometimes with a large number
of flowers.
• The flowering stem can be basal, that is, produced from
the base of the tuber
• As an apomorphy of the clade, orchid flowers are
primitively zygomorphic (bilaterally symmetrical), with
exceptions: like Mormodes, Ludisia and Macodes
10.
11. • The orchid flower, like most flowers of monocots, has
two whorls of sterile elements.
• The outer whorl has three sepals and the inner whorl
has three petals.
• The medial petal, called the labellum or lip , which is
always modified and enlarged, is actually
the upper medial petal.
• However, as the flower develops, the inferior ovary or
the pedicel usually rotates 180 degrees, so that the
labellum arrives at the lower part of the flower, thus
becoming suitable to form a platform for pollinators.
12. • This characteristic, called resupination, occurs primitively in
the family and is considered apomorphic, a derived
characteristic all Orchidaceae share.
• The torsion of the ovary is very evident from the longitudinal
section shown. Some orchids have secondarily lost this
resupination, e.g. Zygopetalum and Epidendrum secundum.
• Apostasia and the Cypripedioideae have two stamens, the
central one being sterile and reduced to a staminode
13. • All of the other orchids, the clade called Monandria,
retain only the central stamen, the others being reduced
to staminodes .
• The filaments of the stamens are always adnate (fused) to
the style to form cylindrical structure called the
gynostemium or column .
• The stigma is very asymmetrical, as all of its lobes are
bent towards the centre of the flower and lie on the
bottom of the column.
15. • Pollen is released as single grains, like in most other
plants, in the Apostasioideae, Cypripedioideae
and Vanilloideae. In the other subfamilies, that
comprise the great majority of orchids, the anther (3),
carries and two pollinia.
• At the upper edge of the stigma of single-anthered
orchids, in front of the anther cap, there is
the rostellum, a slender extension involved in the
complex pollination mechanism.
• As mentioned, the ovary is always inferior (located
behind the flower). It is three-carpelate and one or,
more rarely, three-partitioned, with
parietal placentation (axile in the Apostasioideae).
Anthesis
16. Flowers of the unrewarding orchid Disa nervosa (a) mimic
flowers of the rewarding iris Watsonia densiflora (b)
(Van der Pijil, L. 1972)
17. Pollination
• The complex mechanisms which orchids have
evolved to achieve cross-pollination were
investigated by Charles Darwin.
• Pollinators are often visually attracted by the
shape and colours of the labellum.
Some Bulbophyllum species attract male fruit
flies (Bactrocera spp.)
• The flowers may produce attractive odours.
• Nectar may be produced in a spur of the labellum
(8 in the illustration above), or on the point of the
sepals, or in the septa of the ovary, the most
typical position amongst the Asparagales.
18. In orchids that produce pollinia, pollination
happens as some variant of the following
sequence:
When the pollinator enters into the flower, it
touches a viscidium, which promptly sticks to its
body, generally on the head or abdomen.
While leaving the flower, it pulls the pollinium
out of the anther, as it is connected to the
viscidium by the caudicle or stipe.
19. The caudicle then bends and the pollinium is
moved forwards and downwards.
When the pollinator enters another flower of
the same species, the pollinium has taken
such position that it will stick to the stigma of
the second flower, just below the rostellum,
pollinating it.
20. Deception mechanism in the
Orchidaceae
Sl. No. mechanism Exploited insect behaviour
1 Generalised food deception Food foraging
2 Batesian floral mimicry Food foraging
3 Brood-site imitation Oviposition
4 Shelter imitation Sleep/warmth
5 Pseudoantagonism Territoriality
6 Rendezvous attraction Sexual
7 Sexual deception Sexual
(Van der Cingel,1995)
22. Sexual deception
Pseudo-copulation
Ophrysis pollinated by several genera of solitary
bees and wasps. It emits a pheromone that
mimics the scent of a female pollinator. Males are
highly attracted.
Their repeated attempts at copulation transport
the pollinaria between orchids. Often these
orchids bloom prior to the emergence of the real
females.
25. Ophrys bombyliflora specifically attracts male solitary bees of the genus Eucera by chemical,
visual, and tactile means, and does not seemingly offer any other pollinator rewards
(nectar/ pollen).
Source: http://www.botanicalgarden.ubc.ca/potd/2014/01/ophrys-
bombyliflora.php
26. Orchid bees
• The tribe Euglossini, in the subfamily Apinae, commonly
known as orchid bees or Euglossine bees.
• Most of the tribe's species are solitary, though a few are
communal, or exhibit simple forms of eusociality.
• The genera Exaerete and Aglae are cleptoparasites in
the nests of other orchid bees.
• All except Eulaema are characterized by brilliant
metallic coloration, primarily green, gold, and blue.
• Orchid bees range from 8 to 30 mm (0.3 to 1.2 in) long
• Females gather pollen and nectar as food from a variety
of plants, and resins, mud and other materials for nest
building.
29. Fragrance collection
• Male orchid bees have uniquely modified legs which
are used to collect and store different volatile
compounds (often esters) throughout their lives
• Several flowers from other plant families are also
visited by the
bees: Araceae, Gesneriaceae,Solanaceae,
and Euphorbiaceae contain one or more species
that attract male euglossines.
30. Modified legs
males lack corbiculae, they have characteristic enlarged hind
tibiae. These unusual structures have a hole on the outer side,
which provides access to the spongy compartment within. These
unusual structures play an important role in the storage of
fragrance.
31. • The chemicals are picked up using special brushes
on the forelegs --- middle legs ---- hind legs,
squeezing the chemicals past the waxy hairs
which block the opening of the groove, and into a
sponge-like cavity inside the hind tibia.
• The accumulated "fragrances" are evidently
released by the males at their display sites, where
matings are known to take place.
33. Male Behaviour
• Male orchid bees exhibit a peculiar behaviour of
collecting fragrant volatile compounds from their
environment.
• These compounds are meticulously collected, stored,
and (presumably) presented to females by fanning
their wings and “spray ventilating” their bouquet for
the inspection of prospective mates.
• Fragrant compounds are collected by males with
mop-like protrusions on their front tarsi.
• They are then transferred into the enlarged hind
tibiae through the hole.
34. Nest structure
• Plant resins are used by Euglossa as a
construction material, nest may be either
concealed or aerial.
• In case of E. ignita, the bees actively make or
enlarge cavities in masses of fern roots.
• Other nests are found in ground, termite nests
or in artificial cavities.
• The nests are lined with resin and the
entrance is reduced to a circular opening,
which may be closed with resin at night.
37. Single mating in orchid bees
• Strictly neotropical orchid bees (Euglossini),
monandry (Strassmann, 2001)
• Kin selection theory-- natural selection resulting
from altruistic behaviour by animals towards
members of the same species, esp their offspring
or other relatives (Queller and Strassmann, 1998;
Boomsma, 2007).
• Males forage for volatile chemicals (fragrances)
in a time-consuming and risky manner (Eltz et
al., 1999).
Altruism= behaviour by an animal that may be to its
disadvantage but that benefits others of its kind, as a warning cry that
reveals the location of the caller to a predator.
38. • Flowers of orchids and other plants, as well as
decaying wood or fruits, serve as natural
sources of such fragrances, which consist
mostly of terpenoids and aromatics.
• The male perfume is likely to function as a
species specific chemical signal analogous to
endogenous sex pheromones (Vogel, 1966;
Zimmermann et al., 2006).
• In addition, the individual perfume of a male
could represent a fitness indicator, giving an
approaching female the possibility to evaluate a
male’s quality and to choose her best mate.
39. Fragrance collection, storage, and
accumulation by individual male
orchid bees
• Individually marked males of two species of Euglossa
were sighted repeatedly and over considerable periods of
time (up to 44 days) at artificial fragrance baits exposed
on Barro Colorado Island (BCI), Panama.
1. Do male Euglossini forage for fragrances over long
periods of their lifetime?
2. Are individual males interested in collecting a variety of
compounds as expected from observations at the species
level (Ackerman, 1989)?
40. 3.What quantities and qualities of fragrances are
found in the hind tibiae of individual males
captured at fragrance baits?
4. What happens to the fragrances once they have
been transferred into the hind tibiae? Are males
able to retain the volatiles over time, or are the
fragrances lost, chemically modified or exposed
during display?
5. Is there a relationship between the age of
individual bees and the quantity of fragrances in
their hind tibiae?
41. Mark-Recapture at Artificial Fragrance Baits.
• A total of eight compounds was used: 1,8-cineole
(c), benzyl acetate (ba), methyl salicylate (ms), p-
dimethoxybenzene (p-db), vanillin (v), p-cresyl
acetate (p-ca), terpinene-4ol (t-ol), and t-methyl
cinnamate (t-mc).
• These compounds were previously known to be
good attractants for a range of euglossine bee
species.
(Ackerman, 1989; Whitten, unpublished observations).
• Fragrances were simultaneously exposed on
herbarium blotter pads in the radio tower clearing
on BCI on 25 days (for 2-4 hr between 9:00 and
14:00 hr) between May 31 and July 23 in 1994
(every second day, except on rainy days)
42.
43.
44. • The fragrances can be stored very efficiently in the hind
tibiae over long periods of time. This superior storage
capability is probably achieved through the combined
effects of the retaining properties of the non polar
carrier lipids secreted from the labial glands (Whitten
et al., 1989) and the strong capillary forces imposed by
the sponge-like morphology of the invaginated cuticle
inside the hind tibia that serves as a storage container
( Vogel, 1963, 1966; Cruz-Landim et al., 1965).
• There is a positive relationship between the individual
fragrance quantity and the established age correlate
wing wear in Euglossa cognata.
Results
45. Trichocentrum pumilum: an orchid
pollinated by oil-collecting bees
• The reproductive biology, reward production and pollination
mechanism of Trichocentrum pumilum were studied .
• Trichocentrum pumilum blooms in spring.
• Each paniculate inflorescence bears an average of 85 flowers
that present a central yellow callus and finger-like trichomes
on the lateral lobes of the lip.
46. • A lipoidalsubstanceisproduced and stored among these
trichomes.
• In the studiedpopulation,T.Pumilumisexclusively
visitedand pollinatedby two bee species:
Tetrapediadiversipesand Lophopedianigrispinis
47. Pollinaria are deposited on mouthparts of bees during
collection of the lipoidal substance from the lateral
lobes of the labellum.
Trichocentrum pumilum is self-incompatible and
pollinator-limited.
Natural fruit set was low (9%, compared to 45% in
experimentally cross-pollinated flowers). Potentially
viable seed exceed 97% in fruits obtained through
cross-pollination and in natural conditions (open
pollination).
48. Trichocentrum pumilum. (A) Flower in frontal view. (B) Pollinarium
in dorsal and lateral views. (C) Tetrapedia diversipes visiting a
flower. (D) A
detail of the head of T. diversipes showing a pollinarium attached on
clypeus
Notas del editor
Clitoria javacensis (Fabaceae) is a legume produces a few nectariferous flowers which are visited by large euglossine. Eulalaema meriana is a long tongue bee pollinate the c. lipscombiae orchid which is found in epiphyte of low land moist forests and present in much more restriction.
