Epiphytic orchids in the Southern Cape: Identification by leaf

@milewski @jeremygilmore @justinponder2505 @christiaan_viljoen @malthinus @brendancole

By Ludwig Muller, SCHG (Southern Cape Herbarium, George)
ludwigxem@gmail.com

What are epiphytic orchids?
Epiphytic is best explained here: https://www.merriam-webster.com/dictionary/epiphyte
Basically, it's a plant growing on another plant without being parasitic. The host plant is normally larger than the epiphyte.
Most people, if they think of orchids at all, think of the epiphytic orchids. But here in the Southern Cape the majority of orchids are geophytes/terrestrial.
We are only supposed to have 9 species of epiphytic orchids here, but apparently Aerangis mystacidii has been reported from George and Knysna. Due to a paucity of recent records this species has been excluded, but can be seen here: https://www.inaturalist.org/observations/84737527 and https://www.inaturalist.org/observations/70134699 . Tridactyle bicaudata subsp. rupestris is not included in this article because it never grows on trees. The orchids listed here normally occur in dense Afrotemperate forest, and sometimes in coastal thicket.

The species list, with type specimens, is as follows:
Angraecum conchiferum- https://www.inaturalist.org/observations/99573537
A. pusillum- https://www.inaturalist.org/observations/10798465
A. sacciferum- https://www.inaturalist.org/observations/69713856
Cyrtorchis arcuata subsp. arcuata- https://www.inaturalist.org/observations/102243416
Calanthe sylvatica- https://www.inaturalist.org/observations/71129824
Liparis remota- https://www.inaturalist.org/observations/78057117
Mystacidium capense- https://www.inaturalist.org/observations/96900170
Polystachya ottoniana- https://www.inaturalist.org/observations/10859440
Tridactyle bicaudata subsp. bicaudata- https://www.inaturalist.org/observations/68215956
Note: Liparis remota and Calanthe sylvatica are normally terrestrial. However, you do find the odd specimen growing epiphytically, which is why they're included here.

Now that you know what the local orchids look like, we can deal with imposters.
Firstly, the fern Vittaria isoetifolia can be confused with Angraecum pusillum.
See https://www.inaturalist.org/observations/20291984 and compare with Angraecum observation above.

Next is Lepisorus schraderi, another epiphytic fern. It also grows as a lithophyte on occasion.
https://www.inaturalist.org/observations/68878068
https://www.inaturalist.org/observations/10822306
Compare with Mystacidium and young Cyrtorchis.

Pleopeltis macrocarpa could possibly be identified as an orchid.
https://www.inaturalist.org/observations/77108790

Elaphoglossum ferns are great candidates for confusion. See below:
https://www.inaturalist.org/observations/75070759
https://www.inaturalist.org/observations/103881674
https://www.inaturalist.org/observations/109748996

And finally the Paintbrush lily,Scadoxus puniceus. It sometimes grows as an epiphyte, notably the population on Hoekwil Big tree. See https://www.inaturalist.org/observations/107958850

• Scadoxus is distinguished from epiphytic orchids by the purplish-black spots on the lower stem.
• All epiphytic ferns can be distinguished from orchids by the lack of long, whitish roots clasping the host.

And now we can move on to identifying the orchids themselves.
As before, I have prepared a key. I think it's foolproof, but if you run into any hitches please let me know.

Leaves less than or equal to 8mm wide....... 1.1
Leaves greater than 8mm but less than or equal to 12mm in width....... 2.1
Leaves greater than 12mm wide....... 3.1

• 1.1 Sympodial growth pattern/pseudobulbs present....... Polystachya ottoniana
  -Monopodial growth pattern/pseudobulbs absent....... 1.2

• 1.2 Leaves at least 10 times longer than wide, grass- like, in a terminal cluster....... Angraecum pusillum
  -Leaves not grass- like....... 1.3

• 1.3 Leaf margins not rolled / leaf V-shaped in cross section, stem to 350mm....... Tridactyle bicaudata
  -Leaf margins rolled ever so slightly, stems to 300mm....... 1.4

• 1.4 Plant compact, stem less than or equal to 40mm, 4-8 leaves....... Angraecum sacciferum
  -Plant branching, stem less than or equal to 300mm, 8-16 leaves.......Angraecum conchiferum

• 2.1 Leaf with prominent apical "V", stem less than or equal to 350mm....... Tridactyle bicaudata
  -Leaf lacking prominent "V", stem to 25mm....... Mystacidium capense

• 3.1 Leaves pleated....... 3.2
  -Leaves bilobed....... 3.3

• 3.2 Leaves less than or equal to 100mm long....... Liparis remota
  -Leaves greater than 190mm long....... Calanthe sylvatica

• 3.3 Leaves with prominent apical "V", stem to 400mm....... Cyrtorchis arcuata
  -Leaves lacking prominent "V", stem to 25mm max....... Mystacidium capense

Terminology:
Sympodial growth- https://myfirstorchid.com/2016/07/04/monopodial-and-sympodial-orchids/
Leaf margins rolled- https://woodyplantstutorial.nres.illinois.edu/margins/mar-revolute.html
Apical "V"- a V-shaped indentation at the leaf tip
Pleated leaves- see first image at https://www.birdsoutsidemywindow.org/2018/06/16/pleated-leaves/
Bilobed leaves- https://www.collinsdictionary.com/dictionary/english/bilobate
Lithophytic- growing on rocks

If flowers are present identification will be a lot easier- I was going to make a flower key for this article but decided against it. If you need help with identifying an epiphytic orchid feel free to tag me @ludwig_muller
Note that it is possible, at least in theory, for the forest orchid Bonatea speciosa to grow epiphytically. I have never heard of this happening, but if you do find such a specimen it can be easily told apart from other epiphytic orchids by the prominent black "sheath" clasping the base of the stem. This "sheath" is shown clearly here- 2nd pic from left: https://www.inaturalist.org/observations/107758802
For more information, I would recommend Redlist. See below:
http://redlist.sanbi.org/species.php?species=2762-2 Angraecum conchiferum
http://redlist.sanbi.org/species.php?species=2762-4 A. pusillum
http://redlist.sanbi.org/species.php?species=2762-5 A. sacciferum
http://redlist.sanbi.org/species.php?species=2765-3 Calanthe sylvatica
http://redlist.sanbi.org/species.php?species=2815-1 Cyrtorchis arcuata
http://redlist.sanbi.org/species.php?species=2807-6 Liparis remota
http://redlist.sanbi.org/species.php?species=2790-4 Mystacidium capense
http://redlist.sanbi.org/species.php?species=2770-13 Polystachya ottoniana
http://redlist.sanbi.org/species.php?species=2821-1 Tridactyle bicaudata subsp. bicaudata

And finally, here is the info from Orchids of South Africa by Johnson & Bytebier:
Angraecum conchiferum- 8-16 leaves, adjacent, narrowly strap-shaped, unequally bilobed,
30-60 x 4-8mm, stem to 300mm. Often on Yellowwoods (Podocarpus sp, especially P. falcatus).
A. pusillum- 5-10 leaves, grass- like, linear, rounded, thin, in dense terminal cluster on stem,
40-160 x 3-4mm. Old inflorescences persistent.
A. sacciferum- 4-8 leaves, stiff, nearly erect, flat, linear to strap- shaped, obscurely and unevenly bilobed, 20-60 x 3-7mm. Stem to 40mm. Old inflorescences persistent.
Calanthe sylvatica- Leaves pleated, thin, 200-400 x 70-115mm, plant to 70cm.
Cyrtorchis arcuata- Leaves strap- shaped, folded together basally (Author's note: This trait is not very obvious or reliable), unequally bilobed, pale green, 100-160 x 20-30mm. Stem to 400mm.
Mystacidium capense- leaves strap- shaped, unequally bilobed, 40-120 x 10-22mm. Stem to 25mm.
Polystachya ottoniana- 2-3 leaves per pseudobulb/plant, linear to strap- shaped, 20-130 x 4-8mm. Up to 150mm tall.
Tridactyle bicaudata subsp. bicaudata- Leaves arranged in two opposite rows, leathery, linear to strap- shaped, rounded, unequally bilobed, 60-120 x 7-12mm.

Acknowledgements:
I wish to thank Dr Niels Jacobsen for his guidance and mentorship and Dr Brendan Cole for being so supportive of this project.

References:
Liltved, W., Johnson, S., 2012. The Cape Orchids: A Regional Monograph of the Orchids of
the Cape Floristic Region. Sandstone Publications, Cape Town.
Johnson, S.D., Bytebier, B., 2015. Orchids of South Africa: A Field Guide. Struik, Cape Town
Crouch, N. R., Klopper, R. R., Burrows, J. E., Burrows, S. M., 2011. Ferns of Southern Africa: A comprehensive guide. Random House Struik, South Africa

Publicado el abril 20, 2022 01:15 TARDE por ludwig_muller