![]() ![]() However, evolution shows no mercy with wasters and given the orchids’ success, their seed dispersal strategy must pay off. Shedding millions of seeds most of which go to waste, seems very wasteful. As famously documented, they were among the first pioneers to resettle on the islets of Krakatoa after the catastrophic volcanic eruption of 27 August 1883. ![]() Orchids managed to reach isolated islands far away from the mainland. This does not mean, however, that their seeds are not able to cover long distances. The fact that many orchid species are endemics with very limited distributions supports this theory. Long-distance dispersal would mean that the same amount of seed is distributed over a larger area which could actually lower the odds of encountering a compatible host in a suitable location. Scattering large numbers of seeds with the wind merely heightens the chances that at least some end up in a place where they are lucky enough to meet their specific fungal partner without which they cannot germinate. However, their strategy is not to travel long distances. With their small size, low weight and balloon-testa, orchid seeds are perfectly adapted to wind-dispersal. Their dependence on certain fungal partners is most probably the reason why orchids produce vast numbers of tiny seeds. Few orchids don’t need any fungus at all for their germination, such as certain species of Disa from South Africa, a remarkable exception among terrestrial orchids. Some orchids are able to join up with many different species of fungi whilst others only accept a very specific fungus to enter their lives (or rather roots). They first have to engage in a mycorrhizal relationship with a fungus that helps to feed the emerging seedling. With a little help from their friendsīecause orchid seeds lack a food reserve in the form of an endosperm or a large embryo, most of them, especially terrestrial ones, are generally unable to germinate on their own. Just one single cell layer thick, the seed coat (also called testa) forms a balloon around the embryo, a clear adaptation to wind dispersal. At the time of dispersal, orchid seeds consist of a spindle-shaped, wafer-thin seed coat that encloses an extremely small and simplified embryo in the shape of a spherical cluster of cells. The reduction in seed size and weight is mainly achieved at the expense of embryo and endosperm, the latter failing to develop in orchids. At a ‘gigantic’ 6 mm, the seeds of the lopsided star orchid ( Epidendrum secundum) are allegedly the longest of any orchid. ![]() Those of the New Caledonian species Anoectochilus imitans are said to be the smallest of all, measuring just 0.05 mm in length. According to the literature, there are orchids with even smaller seeds. At around 0.2 mm in length, Aerides odorata has the smallest seeds I have ever come across at Kew’s Millennium Seed Bank. To give an impression of the dimensions involved: a single capsule of the tropical American orchid Cycnoches chlorochilon produces almost four million seeds, and one gram of seeds of the southeast Asian species Aerides odorata contains 3.4 million seeds. A typical orchid seed is merely the size of a speck of dust. What’s more, they also hold the world record for having the smallest seeds of all flowering plants. Famed for their beautiful and fascinating flowers, with over 26,000 species worldwide, orchids are the largest of all flowering plant families. Seeds like dustĪt the other extreme of the spectrum we find the seeds of orchids. It can weigh up to 18 kg and resembles something that, while bobbing in the waves of the Indian Ocean, gave sailors in the Middle Ages all kinds of, well, “seedy” ideas. Famed for both its volume and suggestive shape, the seed (actually a single-seeded stone) of the Seychelles nut or double coconut ( Lodoicea maldivica, Arecaceae) holds the unbeaten record for the world’s largest seed. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |