Holothrix IDs in the Southern Cape based on leaves

@sedgesrock @malthinus @justinponder2505 @ren_hoekstra @christiaan_viljoen @milewski @knysna_wildflowers @tonyrebelo

We all know the frustration that comes from not being able to ID an orchid- especially when there is no flower. For when a flower is present, the Orchids of South Africa makes identification easy, but when the flower is absent there is not, as far as I am aware, a book concentrating specifically on orchid leaves. So this article aims to clear up some of the confusion regarding tricky IDs in the genus Holothrix- based on leaf structure, colour, hairiness, size and shape. All the type observations have leaf pics. I have included 11 species and 2 varieties as occuring in this area, namely:

Holothrix brevipetala- type observation https://www.inaturalist.org/observations/37464114
H. burchellii- type observation https://www.inaturalist.org/observations/97908227
H. cernua- type observation https://www.inaturalist.org/observations/99342981
H. exilis- type observation https://www.inaturalist.org/observations/98610067
H. grandiflora- type observation https://www.inaturalist.org/observations/10980768
H. mundii- type observation https://www.inaturalist.org/observations/92901849
H. parviflora- type observation https://www.inaturalist.org/observations/97642970
H. pilosa- type observation https://www.inaturalist.org/observations/95608185
H. schlechteriana- type observation https://www.inaturalist.org/observations/107177600
H. secunda- type observation https://www.inaturalist.org/observations/98290696
H. villosa var. villosa- type observation https://www.inaturalist.org/observations/99341754
H. villosa var. condensata- type observation https://www.inaturalist.org/observations/107879164

Firstly, we need to exclude some other species and families often confused with Holothrix.
According to https://www.inaturalist.org/taxa/119761-Holothrix, we are faced with the genera
Ornithogalum, Massonia, Satyrium, Eriospermum and Platanthera, an orchid genus from the Northern hemisphere.
I will exclude Platanthera from the start, assuming it does not and never will occur naturally in South Africa, let alone the Southern Cape.
In my experience, Eriospermum and Ornithogalum are the two genera that are most often confused with Holothrix.

Eriospermum examples can be seen here:
https://www.inaturalist.org/observations/77237656 Eriospermum dielsianum
https://www.inaturalist.org/observations/41748832 E. pubescens
https://www.inaturalist.org/observations/49986272 E. capense
https://www.inaturalist.org/observations/24740687 E. vermiforme
https://www.inaturalist.org/observations/11110583 E. brevipes

Observations where Holothrix and Eriospermum have been confused:
https://www.inaturalist.org/observations/95013397
https://www.inaturalist.org/observations/29227821

The two Ornithogalums most frequently confused with Holothrix are dubium and hispidum. See links below:
https://www.inaturalist.org/observations/75938927 Ornithogalum dubium
https://www.inaturalist.org/observations/77584041 O. dubium
https://www.inaturalist.org/observations/77870868 O. hispidum
https://www.inaturalist.org/observations/110642149 O. hispidum

Ornithogalum and Holothrix confusion:
https://www.inaturalist.org/observations/99701654
https://www.inaturalist.org/observations/51998115

Massonias are not generally confused with Holothrix, but confusion does arise at times. See below for typical Massonia examples:
https://www.inaturalist.org/observations/72673295 Massonia longipes
https://www.inaturalist.org/observations/89691522 M. depressa
https://www.inaturalist.org/observations/82992734 M. depressa
https://www.inaturalist.org/observations/82824040 M. setulosa

Examples of Holothrix- Massonia confusion:
https://www.inaturalist.org/observations/77043892
https://www.inaturalist.org/observations/32754037

The orchid genus Satyrium can normally be distigiushed from Holothrix by the large consistently glabrous light green leaves. These are typical examples:
https://www.inaturalist.org/observations/97142151 Satyrium membranaceum
https://www.inaturalist.org/observations/94206185 S. muticum
https://www.inaturalist.org/observations/102163407 S. acuminatum
https://www.inaturalist.org/observations/99341756 S. erectum

The inevitable confusion:
https://www.inaturalist.org/observations/87116912
https://www.inaturalist.org/observations/70733950
https://www.inaturalist.org/observations/85309674

One genus which Inat fails to list as a potential candidate for confusion with Holothrix is Bartholina. I include it here due to its close relationship with Holothrix and the fact that thay co-occur throughout this area. Bartholina differs from Holothrix in several ways with its small single leaf and prominent white veins in etheliae's case.
https://www.inaturalist.org/observations/94472308 Bartholina burmanniana
https://www.inaturalist.org/observations/101685854 B. burmanniana
https://www.inaturalist.org/observations/86025656 B. etheliae
https://www.inaturalist.org/observations/65139309 B. etheliae

Right- now that the other genera and families have been excluded we can get down to the nitty-gritty of Holothrix itself. I have made a simple key specially for this article- please note that the key is not completely foolproof and should not be used out of our area. What I mean when I say that the key is not watertight is simply that some populations of Holothrix cernua out of this region lack leaf hair.

Anyway, here it is. I'm afraid that I could not make a key for use with only leaves, and had to bring flower stalks and the flowers themselves into the picture, but I'll try to amend that with a list culled from Orchids of South Africa later on. I've also tried to make it as user-friendly as possible.

    1. Leaves hairy above....... 2.1
      -Leaves hairless above....... 3.1

  • 2.1 Leaves with "scales" or short hooked hairs....... Holothrix cernua
    -Hairs not hooked, lacking "scales" ....... 2.2

  • 2.2 Hairs on flower stalk deflexed - turned sharply downward....... H. brevipetala
    -Hairs on stalk more or less at right angles to the stalk....... 2.3

  • 2.3 Spur- little tail behind flower- less than or equal to 1.9mm long....... H. exilis
    -Spur greater than 1.9mm....... 2.4

  • 2.4 Lip 3-lobed ( divided in three ), central lobe curved upwards....... H. villosa var. condensata
    -Lip 3-lobed, central lobe no different from the others....... H. villosa var. villosa

  • 3.1 Underside of leaf hairy....... Holothrix pilosa
    -Lacking hair underneath....... 3.2

  • 3.2 Tiny hairs along leaf margin, spur straight....... H. mundii
    -Lacking marginal hair, spur slightly to strongly curved....... 3.3

  • 3.3 Bracts present....... 3.4
    -Bracts absent....... 3.6

  • 3.4 More than 7 bracts....... H. grandiflora
    -No. of bracts less than or equal to 7....... 3.5

  • 3.5 Relatively long deflexed hair on flower stalk....... H. burchellii
    -Hair on stalk, if present, pubescent ( like velvet )....... H. schlechteriana

  • 3.6 Lip 5-lobed ( divided in 5 ), lobes more or less rectangular....... H. parviflora
    -Lip 5-lobed, lobes linear, acuminate ( tapering to a point )....... H. secunda

In case there was any confusion or difficulty using the key, here are some useful tips and definitions:
What are bracts? See https://en.wikipedia.org/wiki/Bract and https://www.merriam-webster.com/dictionary/bract
And spurs? Those tiny "tails"? See https://en.wikipedia.org/wiki/Nectar_spur Also in https://www.inaturalist.org/observations/54393258 the spur is the tiny J-shaped curl visible on the lower 3 flowers.
When a leaf is referred to as being hairless above, what should it look like? See the third pic from the left in this observation: https://www.inaturalist.org/observations/31532859
And when a leaf is hairy above? https://www.inaturalist.org/observations/77229011 and https://www.inaturalist.org/observations/100227957 are prime examples of upper surface hairiness.
And what do hairy margins look like? ( article 3.2 ) See https://www.inaturalist.org/observations/92901849
And lip lobes? See the illustration of Orchis italica here: https://en.wikipedia.org/wiki/Labellum_(botany)

Info from the Orchids of South Africa and the Cape Orchids:
Holothrix breviptala- leaf pressed flat, hairy with stout hairs, less than or equal to 12mm in width
H. burchellii- leaf pressed flat against the ground, less than or equal to 60mm broad
H. cernua- leaf pressed flat, covered with short, stiff, hooked hairs above, less than 30mm broad
H. exilis- leaf pressed flat, sparsely hairy above, leaf width uncertain, probably 18mm wide
H. grandiflora- leaf pressed flat, glabrous, less than or equal to 80mm broad
H. mundii- leaf pressed flat, glabrous, short marginal hairs present, less than 21mm wide
H. parviflora- pressed flat or slightly raised, glabrous,less than or equal to 30mm wide
H. pilosa- leaves flat, upper surface glabrous, underside and margins hairy, less than 145mm wide
H. schlechteriana- leaf pressed flat to the ground, glabrous, less than or equal to 100mm wide
H. secunda- leaf pressed flat, glabrous, width uncertain, probably less than 80mm wide
H. villosa- both varieties- leaf pressed flat with a sparse to dense scattering of long hairs on upper surface, less than or equal to 95mm

Further reading:
http://redlist.sanbi.org/species.php?species=2841-2 Holothrix brevipetala
http://redlist.sanbi.org/species.php?species=2841-3 H. burchellii
http://redlist.sanbi.org/species.php?species=2841-4 H. cernua
http://redlist.sanbi.org/species.php?species=2841-9 H. exilis
http://redlist.sanbi.org/species.php?species=2841-12 H. grandiflora DDD
http://redlist.sanbi.org/species.php?species=2841-20 H. mundii
http://redlist.sanbi.org/species.php?species=2841-22 H. parviflora
http://redlist.sanbi.org/species.php?species=2841-24 H. pilosa NT
http://redlist.sanbi.org/species.php?species=2841-27 H. schlechteriana
http://redlist.sanbi.org/species.php?species=2841-29 H. secunda
http://redlist.sanbi.org/species.php?species=2841-32 H. villosa var. condensata
http://redlist.sanbi.org/species.php?species=2841-33 H. villosa var. villosa

Publicado el jueves, 14 de abril de 2022 a las 01:01 PM por ludwig_muller ludwig_muller

Comentarios

Oh- the reason I added all those type observations was to give readers a baseline from which to start when reading the article. Each observation showcases features unique to the orchid in question, which is really the purpose of type specimens in herbaria.

Anotado por ludwig_muller hace casi 2 años

It might be worth noting that brevipetala, exilis and to a lesser extent villosa var. condensata are all much taller and racemose/sparsely flowered in our area.

Anotado por ludwig_muller hace casi 2 años

Thanks Ludwig - looks like a great piece of work. I will trawl through it soon.

Anotado por knysna_wildflowers hace casi 2 años

This looks like a really useful contribution. Many thanks to you, Ludwig.

Anotado por milewski hace casi 2 años

Brilliant Ludwig. Really well thought through and presented. Love the key! What about a paper version for the SC Herbarium…?

Anotado por brendancole hace casi 2 años

Thanks for all the positive comments!
I'll see what can be done about the SCHG article.

Anotado por ludwig_muller hace casi 2 años

Well done, that is a fair amount of work and research! Thanks for sharing your efforts. You are becoming quite the orchid expert!

Anotado por christiaan_viljoen hace casi 2 años

Whoa! Error in the Key! I recently found a Holothrix population- unidentified- which would be keyed out as pilosa in the Key. It is not pilosa. See https://www.inaturalist.org/observations/122947166

Anotado por ludwig_muller hace más de un año

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