|MadSci Network: Botany|
You are correct that pines could not "know" exactly when Easter was approaching given that Easter is a movable holiday. However, new shoot growth in pine occurs in spring so in some locations there is some correlation of new growth to Easter. However, some pines, such as Pinus ponderosa, are native from Mexico to Canada. In Canada, Easter would probably occur before early pine growth and in Mexico, Easter would probably occur after early pine growth. . New shoot growth in pines may superficially resemble a cross because the terminal shoot is vertical and there are usually at least two lateral shoots that are roughly perpendicular to vertical. However, there are usually more than two lateral shoots so it is not just a simple cross as seen in the photo in the first reference.
There may also appear to be a slight bit of truth to stories about plant growth correlating with certain holidays only because plants can tell what time of year it is. Plants tell time based on the photoperiod or relative length of the daily light and dark periods. The pigment phytochrome is used by plants to sense the photoperiod. By artificially manipulating the photoperiod, people can get photoperiodic plants to bloom at any time of the year. For example, chrysanthemums naturally bloom in the short days of autumn but are now brought into flower yearround by artificially shortening the daylength at other times of the year and using greenhouses in the winter.
There are many plants that naturally bloom roughly near certain holidays such as poinsettia (Christmas), Christmas cactus, Easter cactus, and Thanksgiving cactus. However, there is no scientific evidence that they bloom at that time because of the holiday. Scientists would interpret the bloom time as simply having evolved to bloom at that time of year perhaps because of the favorable weather or availability of pollinators. Given that the seasons are reversed between the Southern and Northern hemispheres, plants that bloom for a particular holiday in one hemisphere probably would not bloom for that holiday when grown in the other hemisphere.
There are many legends or symbolisms involving plants and religion, such as the passionflower symbolizing several aspects of the passion of Christ, dogwood's supposed use for the cross Christ was crucified on and Easter lilies appearing in Christ's empty tomb. Those kinds of stories are not scientific. There is no way yet known for a scientist to prove that someone did not just make up the legends about plants and religion. You could pick many plants and correlate the number of flower parts or the structure of the plant to some Biblical or religious event.
"Pine tree cross" photo
Pinus ponderosa range map
Photoperiodism and Phytochrome
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