This entry was schedule to appear yesterday. Unfortunately an unknown problem arose and it did not appear as scheduled. My apologies.
Today's entry was written by Randal Mindell, a botanist working on a special project at UBCBG. Randal took the close-up photo and I took the full view. Randal writes:
Fronds of Osmundastrum cinnamomeum (cinnamon fern) come in two forms: tripinnate vegetative fronds and tripinnate reproductive fronds. This differs from the coupling of reproductive structures on vegetative, photosynthetic leaves common to the vast majority of filicalean ferns. The distinction between the two frond types is easy to see in the picture, with tan fertile material encircled by traditional, verdant foliage. If you feel like you have seen this before, perhaps you are thinking of other erect and iconic ferns such as Blechnum spicant (deer fern), Onoclea sensibilis (sensitive fern) or Matteuccia struthiopteris (ostrich fern).
Among living ferns, the family Osmundaceae has one of the longest fossil records. It traces back to the Paleozoic, and is widely distributed across the northern hemisphere during the Mesozoic. Given the widespread nature of Osmunda cinnamomea in the present (North & South America, Asia), I would like to reflect on the reproductive potential that fuels its dispersal. Plants here at the garden give off anywhere from 5-10 fertile fronds. An informal count revealed that these fronds produce anywhere between 11-19 pairs of primary pinnae (primary divisions of the leaf), which in turn give off anywhere between 13-20 pairs of secondary pinnae. Counting the tertiary pinnae (the sterile tissue on to which the sporangia are borne) is too painful, but a count of sporangia on a few secondary pinnae averaged 45 per pinna. Putting these loose numbers together (fertile fronds × primary pinnae × secondary pinnae × sporangia per secondary pinna) and multiplying them by the 64 spores per sporangium that is standard for the Dryopteridaceae, we see that one individual has the potential to produce anywhere from 8-43 million photosynthetic spores.