Issue 3 2013 Lo-res PDF - Passion Flowers

Peduncle length
When grown indoors, the flowers and foliage of P. ‘Amethyst’ appear similar to outdoor
specimens except that outdoor cultivation generally produces plants with shorter peduncles.
Figure 4 shows the frequency distribution of peduncle length for the two groups. Measurements,
to the nearest 0.1cm, were made 1-3 days following anthesis in July and August. Most outdoor
peduncles were less than 9cm, whereas indoor peduncles were usually more than 9cm. The
mean lengths of the two samples were 7.83cm (N = 89) and 9.66cm (N = 67) respectively. The
difference (1.83cm) is statistically significant (P < 0.0001).
Discussion
Frequency distribution of peduncle length in P. ‘Amethyst’ for plants grown outside and
inside
The increase in peduncle length of P. ‘Amethyst’ under low light might be detectable with
other cultivars, and is presumably a form of etiolation, an effect caused by low light levels
leading to pale spindly growth. The purple colouration of new growth may be an adaptation
to protect against light damage, while higher light levels will lead to greater starch production
in leaves and a consequent increase in size and thickness.
The differences described here may have wider significance. The morphological descriptions of
some plants, such as in cultivar registration, could be unreliable when used to identify plants
grown under different conditions. It is also possible that similar effects might be present in
wild-collected specimens of Passiflora species, where light levels at the forest floor are usually
much lower than those at forest edges or in the canopy. The wide range in peduncle length of P.
‘Amethyst’ (5.5cm to 13.5cm) and seasonal variations in both flower colour and shape might
occur in other species and hybrids, and casts doubt on the value of a single measurement of
any aspect of a plant when characterising the morphology of a specimen.
Dr Les King is a chemist and forensic scientist and an amateur Passiflora grower. He was the
Passiflora Cultivar Registrar from 2004 to 2011. http://www.passionflow.co.uk/reg.htm
Dr Les King
a leading chemist and forensic scientist and an amateur Passiflora
grower. He was the cultivar Registrar from 2004 to 2011.
www.passionflow.co.uk/reg.htm
26 Passiflora Online Journal February 2013
Passiflora Online Journal February 2013 27