Platanthera grandiflora Versus Platanthera psycodes

Platanthera grandiflora (Figs. 1, 2, 3) Platanthera psycodes (Figs. 4, 5, 6)

Platanthera psycodes (Bigelow) Lindley and Platanthera grandiflora (Linnaeus) Lindley , with their superficial similarity, are a source of challenge and confusion for nature enthusiasts and botanists alike. Platanthera shriveri P.M. Brown (Fig. 9), a controversial taxon first described in 2009, is separated from P. grandiflora by the following characteristics, as described in a segment of the key presented in "A New Species of Fringed Platanthera From the Central Appalachian Mountains of Eastern North America" (Paul Martin Brown, Clete Smith & J. Scott Shriver): "lip segments deeply and compoundly lacerate; isthmus slender, length ca. 4 times the width; spur 2-2 1⁄2 times the length of the lip; orifice angled at top."

Some experts have chosen to recognize Platanthera shriveri as an ancient hybrid between Platanthera lacera and Platanthera grandiflora, while others believe P. shriveri to be one and the same as Platanthera grandiflora.

Platanthera ×enigma P.M. Brown was described as a hybrid between Platanthera grandiflora and Platanthera psycodes and can be found in areas where the flowering time of Platanthera grandiflora and P. psycodes (which typically flowers later than P. grandiflora) overlap. Mixed populations in Maine, which is one such area, should be examined closely!

Both Platanthera grandiflora and Platanthera psycodes are known to produce flowers that are white (Platanthera grandiflora (Bigelow) Lindley f. albiflora (Rand & Redfield); Platanthera psycodes (Linnaeus) Lindley f. albiflora (R. Hoffman) Whiting & Catling) Catling or pink (Platanthera grandiflora (Bigelow) Lindley f. carnea P.M. Brown; Platanthera psycodes (Linnaeus) Lindley f. rosea P.M. Brown) Forms of P. grandiflora with an entire lip (Entire-lip form: Platanthera grandiflora (Bigelow) Lindley f. mentotonsa (Fernald) P.M. Brown), as opposed to being fringed, are known to occur and have been confused with Platanthera peramoena (A. Gray) A. Gray. A similarly fringeless form of Platanthera psycodes (Platanthera psycodes (Linnaeus) Lindley f. varians (Bryan) P.M. Brown), is also known to occur.

The most reliable characteristics one can use are the shape of the orifice (the opening to the spur/nectary/mentum) and the shape of the rostellum lobes. Platanthera psycodes has an opening shaped like an transverse oval/dumbell (Figs. 6, 7), while Platanthera grandiflora has a rounded opening (Figs. 2, 8). As for the rostellum lobes, Efloras.org sums it up perfectly in couplet 6 of their key to Platanthera. P. grandiflora is described as having "Rostellum lobes spreading, angular in lateral view.", and P. psycodes is described as having "Rostellum lobes parallel, rounded in lateral view."

The raceme on Platanthera psycodes is more slender than that on Platanthera grandiflora, often producing far more flowers of a smaller size and tapering off to a point (with the buds) at the top. It is important to note that flowers on the lower portion of the raceme on P. psycodes usually shrivel before flowers on the upper portion break bud, in contrast to P. grandiflora, where all the flowers on the raceme end up open simultaneously. It is also important to note that, when viewed from above, the raceme on P. psycodes also appears remarkably circular.

The labellum, or lip, is a specialized petal found on all orchid species, serving a variety of purposes and is often integral to the flower's pollination. In Cypripedium , the labellum is pouch-shaped (hence the name "Lady's-slippers"), on Calopogon , it is hinged. Some Platanthera species have a labellum that is entire and unlobed (e.g. Platanthera dilatata), while others have a labellum that is unlobed and fringed (e.g. Platanthera blephariglottis, or, as in Platanthera grandiflora and Platanthera psycodes, three-lobed and typically fringed.

The labellum on Platanthera grandiflora is usually deeply fringed and the lateral lobes (Fig. 3) are dramatically upswept. This is very different from that on Platanthera psycodes, which has far less fringing on the margin and lateral lobes (Fig. 5) that aren't, or are hardly upswept at all, sometimes even appearing to droop down.

As always, use the shape of the opening and rostellum lobes whenever possible, as they are the most reliable, but keep the other characteristics in mind. I'm not sure how reliable it is to use habitat, but I have noticed that Platanthera grandiflora seems to grow more commonly in forests than Platanthera psycodes, which seems to prefer very wet, open areas.

Below are all of the mentioned forms:

White flowered form: Platanthera psycodes (Linnaeus) Lindley f. albiflora (R. Hoffman) Whiting & Catling
Pink-flowered form: Platanthera psycodes (Linnaeus) Lindley f. rosea P.M. Brown
Entire lip-form: Platanthera psycodes (Linnaeus) Lindley f. varians (Bryan) P.M. Brown
White-flowerd form: Platanthera grandiflora (Bigelow) Lindley f. albiflora (Rand & Redfield) Catling
Pink-flowered form: Platanthera grandiflora (Bigelow) Lindley f. carnea P.M. Brown
Entire-lip form: Platanthera grandiflora (Bigelow) Lindley f. mentotonsa (Fernald) P.M. Brown


Fig. 7. Platanthera psycodes, showing the opening and rostellum lobes.


Fig. 8. Platanthera grandiflora, showing the opening and rostellum lobes.


Fig. 9. Platanthera grandiflora/Platanthera shriveri, showing the opening, rostellum lobes and nectary.

Posted by arethusa arethusa, October 26, 2018 20:36

Comments

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@tsn, @cgbb2004... I made this with the two of you in mind. Hopefully it helps!

Posted by arethusa 12 months ago (Flag)
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Excellent! Very helpful. Thank you so much!

Posted by tsn 12 months ago (Flag)
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Great article (and artwork) keep it up!

Posted by afid 12 months ago (Flag)
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Thank you for creating and sharing this truly impressive and helpful guide to these tricky (but lovely) species! Wonderful work!

Posted by cgbb2004 12 months ago (Flag)
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This is so helpful - thank you! You helped me differentiate between these 2 species last year, and this write-up is going into my reference materials.

Posted by catherineklatt 12 months ago (Flag)
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I'm so glad you all like it!

@fatroosterfarm, this was made with you in mind as well. I look forward to seeing what you think!

Posted by arethusa 12 months ago (Flag)
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holy crap, you are so talented! i think you should approach chelsea green publishers with your work. with two inches of wet snow on the ground, my mind wanders toward finding orchids next year...my biological training is in the animal kingdom, so botany at this level is very new to me. thanks to you, @cgbb2004 and @tsn, i have really learned so much in the last three years.

Posted by fatroosterfarm 12 months ago (Flag)
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I have linked this to both taxa to make it easier to find - in the About tab under More Info.

Posted by eraskin 7 months ago (Flag)
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Wow, thank you @eraskin. I feel honored to have both of my identification posts linked to their respective taxa on the site.

Posted by arethusa 7 months ago (Flag)
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Excellent article! Thank you so much for writing this!

Posted by smpbiologist-cpoling 3 months ago (Flag)
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This is really beautiful work. And I like the bonus crab spider. The illustrations really highlight the differences well. For me, visuals are more helpful than words, since I have no formal training and find myself having to look up the definitions of too many words to make keys useful.

Posted by ashley_bradford 2 months ago (Flag)

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