A pH- dependent plant
One of the world’s most popular
ornamental flowers conceals a bouquet of biological and biochemical surprises.
The iconic “snowball” shaped blooms of Hydrangea
macrophylla (big-leafed hydrangea) .
Their species are likewise known for their
bountiful, showy, long-lasting blossoms, making them popular for both
landscaping and the cut flower market.
For starters, the bloom of the hydrangea is
not a true flower, but an inflorescence: Sepals, or
modified leaves, make up most of the bloom and overshadow the small, almost
unnoticeable fertile floral portions at the center.
The bloom
colors are what really make the hydrangea stand out: They range from pink to
blue, including all shades of lavender to violet to purple, as well as green
and white. Color intensities run the gamut from vibrant to pastel.
Hydrangea colors are not what they seem,
either; they are not the result of a variety of different pigments, as is the
case for flowers such as roses or tulips.
The color of many hydrangea blooms acts as a
natural pH indicator for the soil in which the plant grows. Such blooms have
blue sepals when the shrub grows in acidic soil, but develop red or pink sepals
when grown in neutral to basic soils. The hydrangea’s bloom color reveals the
pH of the soil, but with its distinguishing colors being the reverse of those
for litmus paper. The hydrangea is unique among plants in this ability to
indicate soil acidity.
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