Banoth Madhu: Heteranthery in Plants. Heteranthery refers to a state where a single flower carries stamens of two (or more) distinct types, differing in color, size, pollen content, shape, or scent profile (or combinations of these traits) and consequently, in attractiveness to pollinators. Heteranthery has evolved in 12 orders (more than 20 families) across angiosperms and is commonly associated with bee-pollinated, nectarless flowers

1. Heteranthery in Plants
Banoth Madhu
Ph.D Research Scholar
Genetics and Plant Breeding
Tamil Nadu Agricultural University, Coimbatore

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 Heteranthery refers to a state where a single flower carries stamens of two (or
more) distinct types, differing in color, size, pollen content, shape, or scent profile
(or combinations of these traits) and consequently, in attractiveness to pollinators
(Vallejo-Marín et al. 2009, Solís-Montero et al. 2018).
 Heteranthery has evolved in 12 orders (more than 20 families) across angiosperms
and is commonly associated with bee-pollinated, nectarless flowers (Vogel, 1978;
Buchmann, 1983; Endress, 1994; Jesson & Barrett, 2003).
 It provides an opportunity to investigate how differentiation in anther form and
function may reduce the fitness costs of using male gametes as food for pollinators.

4.  Heterantherous species usually lack nectar and offer pollen as the sole reward to visitors,
which are mainly pollen collecting bees (Vogel, 1978; Vallejo-Marın et al., 2009).
 Pollen dispersal in heterantherous species frequently involves buzz-pollination in which
pollen is released from anthers through small apical pores (poricidal anther dehiscence) as
a result of vibrations of flight muscles of the wings of bees (Buchmann, 1983)
Why is Heteranthery rare?
 Excess pollen consumption may not be detrimental to plant fitness and thus there is
no selection for anther specialization and dimorphism.
 Limited availability of sites for pollen placement may constrain the ability to partition
the pollinator’s body among closely related species, thus disfavoring diversification
through sexual specialization.

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Anther types Position Colour Size References
First type
centrally located
in the flower
brightly coloured
stamens (usually
yellow)
short in length
Muller, 1883;
Vogel, 1978.
Second type
away from the
central axis of
the flower
cryptically
coloured
larger in size
than the first type
Vallejo-Marın et
al., 2009; Barrett,
2010
Third type centrally located
Light red and
consist of
staminodes (e.g.
Commelinaceae)
slightly larger
than both
Whalen, 1979;
Luo et al., 2009.
Table: Floral morphology and anther differentiation in two
heterantherous species of Solanum (Solanaceae)

6. Fig. 1 Floral morphology and anther differentiation in two heterantherous species of Solanum.
(a) Solanum rostratum; (b) Solanum citrullifolium., pollinating anther; FA, feeding anthers; S, style.
(Barrett and Vallejo-Marin et al., 2010)

7.  Comparative analyses of monocotyledonous groups have revealed that heteranthery
is commonly associated with enantiostyly (mirror-image flowers, a floral
polymorphism in which the style is deflected to either the left or right side of a flower,
with at least some anthers commonly (but not exclusively) positioned on the opposite
side of the flower and aspects of perianth symmetry and floral orientation (Graham &
Barrett, 1995; Jesson & Barrett, 2003).
 These associations strongly suggest that heteranthery represents a convergent floral
syndrome that has evolved as a result of pollinator-mediated selection.

8. Table; For each pair of traits two models were compared, one in which the two traits evolve independently of each other
(independent model) and the other in which the transitions among characters states in one trait are dependent on the
character state of the other trait (dependent model).
P-values are shown in parentheses and are based on a v2 distribution with 4 df. To account for uncertainty in
phylogenetic reconstruction, likelihood ratios and P-value were calculated for each of 1000 trees representing random
resolutions of polytomous branches in the original phylogeny.
Vallejo-Marın et al., 2010

9. Fig. 2 Phylogenetic relationships among families containing heterantherous species.
Heteranthery (H), poricidal anthers (P), nectaries (N) and enantiostyly (E).
(Barrett and Vallejo-Marin et al., 2010)

10.  The number of species in each family for which heteranthery has been reported varied
enormously.
 Heterantherous families tend to have few stamens and all except two families –
Anacardiaceae and Brassicaceae – contain species with poricidal anther dehiscence.
Nectaries occur in all but three families (Commelinaceae, Dilleniaceae and
Malpighiaceae), although heterantherous taxa most often lack nectar.
 With respect to floral symmetry, 10 out of 16 families with heteranthery possess slight
to strongly zygomorphic perianths, at least occasionally.
 Conclusion; Finally, insects are the main pollinators of families with heteranthery,
and pollen-collecting bees in particular are the most common pollinators and basis of
heteranthery evolution.