I've been away and only just got round to seeing OGD Vol 6, Issues 49, 50 & 51.
Michael Corn was "looking for information or other references with respect to whether the pollinator has been identified and studied for Den. cruentum or similar species in Section formosae (e.g., Den. suzukii, Den. tobaense, Den. ayubii, Den cariniferum)." Steve Beckendorf responded with: "It may be that D. cruentum, like the vast majority of orchid species, doesn't have an identified pollinator. However, it has a couple of characters that suggest it is bird pollinated. Red is a color that attracts birds (often used in the US to attract hummingbirds - I'm not sure what the counterpart would be in Thailand, honeycreepers?). Insects, on the other hand, are usually unable to see red." Michael, I know of no studies in this area. As Steve says, hardly anything is known about the pollination mechanisms of the vast majority of orchids. S.E.Asia does not have a direct equivalent of the New World hummingbirds or the Hawaiian honeycreepers. The bird groups that come nearest would be sunbirds, spiderhunters and flowerpeckers, all of which are mainly insectivores that supplement their diet by taking nectar from flowers. As far as I'm aware, none of them have ever been seen taking nectar from orchids, let alone pollinating them. Sunbirds certainly visit orchids, but only to bathe on any water that has collected on their leaves. Steve may be right when he says that insects are usually unable to see red, but before dismissing insects as possible pollinators I'd like to see the results of examining these flowers under UV & IR light. It is quite possible that the red & white-green combination creates a honeyguide that is visible under either UV or IR. In photography, strong red filters are used to mask visible-light and allow IR to be seen more clearly. Iris chipped in with: "As far as I know, the cruentum group are cool growing (I can't grow most of them in my warm conditions). Many orchids in cool locations where there is not an abundance of insects have evolved bird pollination. Now the experts will tell me if I am all wet about D. cruentum. Sorry Iris, you're wet about both D. cruentum and D. tobaense. Michael was correct when he said that D. cruentum originates from the lowlands of Thailand ... it has a very restricted range, occurring only across the neck of the Isthmus of Kra (see the map on page 60 of my book "A to Z of S.E.Asian Orchid Species") and needs continuous warm conditions that are moist & humid almost all year-round. Daytime temps average 28-32 degrees, dropping by 2-4 degrees at night. Hardly any annual temp variation. D. tobaense occurs in pine forests on Sumatra from 700-1500 metres altitude. It likes conditions that are only 3-4 degrees cooler than you get in D. cruentum's home range ... I think you'd call it "intermediate to warm", certainly not "cool". Check page 76 of my "A to Z" book. Michael was more right than he knew when he said that "D. suzukii, sometimes called the Giant Cruentum, may or may not be a separate species". It isn't a species at all. It is a primary hybrid between D. cruentum and D. tobaense, and it's correct (registered) name is Dendrobium Peng Seng. I know the AOS has awarded a plant under the name "D. suzukii" ... someone didn't do their homework, did they ? Guido would be laughing if he could read this.... yet another example of what he's been saying for years. Cheers, Peter O'Byrne _______________________________________________ the OrchidGuide Digest (OGD) [EMAIL PROTECTED] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
