Tuesday, July 5, 2016

The Largest/Longest Orchid Seeds?

On 29 June I received a box from a really nice friend.  Thanks friend!  The box contained some super neat mini Tillandsias and a couple tubes of orchid seeds...

Epidendrum wrightii
Schomburkia undulata

The Epi is a species of reed-stem so I was very curious whether its seeds are as exceptional as the other reed seeds that I've sown.  My friend had informed me that the wrightii seeds contain lots of "cotton".  This was interesting to hear because I typically associate cotton with monopodial orchid seeds.  When I saw the wrightii seeds they did indeed look like they had lots of cotton.  Upon closer inspection I realized that, unlike with monopodial orchid seeds, the wrightii cotton was actually part of the seed!

The seeds with long "tails" are the wrightii seeds.  Interspersed with the wrightii seeds are seeds from Epi radicans x Epc Orange Blaze.  Above the penny are seeds of Schomburkia undulata.

Here's what the wrightii seeds looked like after I soaked them for one night...

They clumped together just like Tillandsia seeds do when you put them in water.  Perhaps soaking before sowing isn't the best approach for wrightii seeds!

Here's some basic info about orchid seeds...

The orchid seed has no endosperm.  The seed consists of a simple, dry outer coat with a small mass of undifferentiated cells which form a pro-embryo.  This unit can be easily carried in air currents and may travel long distances before coming to rest.  - Calaway Dodson, Robert Gillespie, The Biology of the Orchids

Some more info...

Numerous mechanisms and devices promote appropriate carriage and secure anchorage.  The buoyancy of orchidaceous "dust" seeds is due not only to small size but also to a large airspace between embryo and testa; wall sculpturing and overall shape (usually fusiform) also help to keep them aloft and may encourage attachment to rough bark.  Tillandsioid bromeliad seeds feature hooked coma hairs for better attachment; similar devices on a much smaller scale adorn microsperms of shootless Chiloschista. - David Benzing, Vascular Epiphytes


Experiments indicate that buoyancy and mobility correlate with the apportionment of mass between the coma and the seed proper.   - David Benzing, Bromeliaceae: Profile of an Adaptive Radiation
More broadly, the epiphytes achieved relatively low terminal velocities at least in part because they allocate proportionally more biomass to the coma vs the seed proper.  Percentages (60.0-61.7%) of the aggregate seed mass represented by the flight apparatus grouped the obligate (T. utriculata and T. fasciculata) and faculative (T. ionochroma) epiphytes together, with saxicolous T. sphaerocephala (41%) as the outlier.  In short, the more consistently bark-dependent the taxon, the greater the relative cost of the coma, the more buoyant its seeds, and the greater the dispersal range.  - David Benzing, Bromeliaceae: Profile of an Adaptive Radiation

All Tillandsia seeds have endosperm.  This makes them heavier than orchid seeds.  In order to achieve greater buoyancy and travel greater distances... the Tillandsia seeds have "parachutes"... aka "comas".  The larger the coma, the more epiphytic the Tillandsia.

Does Epidendrum wrightii have a coma?  Kinda?  We can guess that the point of these appendages is to increase buoyancy and to help the seeds attach to bark.  But why don't other orchid seeds have these appendages?  Maybe they don't need them because they aren't as heavy as the seeds of Epi wrightii?  This would imply that, unlike orchid seeds, the seeds of Epi wrightii do have at least some endosperm.  And if most reed-stem Epis do have some endosperm... then we can guess that Epi wrightii is more epiphytic than most reed-stems.

According to Wikipedia (and Arditti and Ghani)... Epidendrum secundum has the distinction of having the longest seeds in the orchid family... 6.0 mm long.  Let's take another look at the comparison photo I took...

The penny is 19.05 mm in diameter... or around three Epi secundum seeds.  In the above photo we can see that the seeds of the Epi radicans cross have a short tail.  We can guess that Epi secundum seeds have a longer tail.  We can also guess that this is what Arditti and Ghani included in their measurement of the Epi secundum seeds.  So if we're including tails in the measurement of orchid seeds... then the seeds of Epi wrightii are a lot longer than the seeds of Epi secundum.

Are there any reeds with seeds that are longer than wrightii?  If so, then this would imply that they were more epiphytic than wrightii.

There are numerous species of reeds and I've only see a very small fraction of their seeds.  Hopefully this post will encourage people to share photos of their reed seeds.

It's really exciting to discover that wrightii seeds are somewhat similar to Tillandsia seeds.  This gives us some material that's potentially very useful in terms of breeding for orchids that are more epiphytic but have seeds that are easier to germinate (don't require flasking).

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