Keying Out a Mustard Part 2

This has been sitting in the stack for several weeks now, just waiting for a little editing. Now that my hands are starting to recover from carpal tunnel syndrome, I am finally getting it out the door.

In the first part of this series I started down the wrong branch of the key from the very first step. Now that I have the initial problem straightened out, let's see where we can get to. (Thanks again Kitty for the comments in italics.)

(Again I am using Hitchcock and Cronquist's Flora of the Pacific Northwest if you would like to follow along)

With the sessile fruit (1b), the next choice is (5b): pod uniform, not divided crosswise into 2 segments (this threw a bit as I wasn't certain at first which direction they meant by crosswise, but the illustration made it clear enough).

I find the illustrations in the key very useful, probably more useful than the glossary.

The next choice was even easier: the fruit is a silique (long and thin) rather than a silicle (closer to round) (6b).

Petals are white (12b).

It would be easy to get caught up in the difficult terminology in the next choice (and I did go through it when keying out initially), but we can simply note that our plant does not fit into the more easily understood criteria (e.g. petals are not 11-15 mm) so we make our choice (13b).

The petal size is probably the most straightforward of the criteria, but the description included in the couplet "grayish with branched hairs; petals...pinkish to purple" and the habitat were also good clues that 13b was the correct choice.

The next split is on whether the seeds are uniseriate or biseriate (a single series or a double series). This was a little confusing to me because the fruit has a series of seeds on each side - so there are two series of seeds, but each series is in a single line. The illustrated glossary that I use pictured biseriate as being two series in the same enclosure (e.g. a row of seeds attached to the top of the enclosure alternating with a row of seeds attached to the bottom - like a zipper). Based on that interpretation (that the fruit contained two sets of uniseriate seeds) I jumped to group VII.

The comparison to a zipper seems particularly useful.

The next choice (74b) was easy to make based on size of the petals and seeds, but I would like to point out the word torulose (just for fun).

I kind of like connivent: converging or coming together, but not organically united.

This is a good spot to point out that sometimes it is easy to choose a couplet based on familiarity with a genus. More simply put, if you know it isn't a Hesperis, take the other lead. This doesn't always work though...

Siliques of this plant are dehiscent (75b) - another common name for the plant (probably the genus in general) is shotweed: when the plant dries, the little panels holding the seeds in will often spring back at a touch, shooting the seeds out like shot.

So if you don't know that the fruit are dehiscent; it might be wise to look at the two genera included under 75b. We can eliminate Raphanus because the fruit are not torulose. Streptanthella can be eliminated by the leaves (the drawing included with the genus was helpful, as was the description)

Leaves are definitely not entire (77b).

This one's a bit tricky: Pubescence (hair) simple or branched? With the size of the hairs on these plants this probably needs some magnification. With a fresh sample I might have been able to eyeball it, but a hand lens would definitely be in order. My microscope was handier today, and all the hairs I could see on my dried out sample were simple (78a).

The hairs visible in the photo were not branched. The photo was quite useful for identification.

Siliques much less than 5cm (79b).

I focused on the calyx not being urn-shaped and the features of the petal

Stem leaves all pinnate (81a), (82b) which takes us to the genus Cardamine.

I will leave determination of the species to the final part of this series.

The species determination should be interesting.

first part of the series

Keying Out a Mustard Part 1

On my recent Nature Quiz I asked about the identification of a plant that grows in my neighborhood. I was pretty confident about its genus already, but getting down to the species level can be a little tricky sometimes. I was planning on being a wimp and just giving the answer at the genus level that I was comfortable with, but Kitty's comment inspired me to go and try to key it out.

I ran in to some trouble. Kitty kindly agreed to provide some analysis/commentary which is in italics throughout the post.

I used Flora of the Pacific Northwest (Hitchcock & Cronquist) with a bit of help from Plant Identification Terminology An Illustrated Glossary (Harris & Harris). Rather than jump to the genus I believed it was, I started at the Cruciferae (mustard) family level.

Trouble right away. The first fork of the key was:

1a Fruit stipitate (stipe as least 1mm) (Stipe means stalk supporting a structure)
1b Fruit Sessile or subsessile (stipe < 1mm)



I had scanned ahead to see where I wanted to end up and this was taking me down the wrong fork. But what the heck, might as well follow what the plant and key tell me rather than my preconceived notions.

I could clearly see a stalk supporting the fruit that was around half a centimeter long, so I chose 1a.

In this case stipitate refers to a stalk associated with the fruit, not the short stalk that connects the fruit to the main stem. If you look at the drawings in the H & C key, there is a clear join between the stalk subtending the fruit and the stalk that connects to the stem. I took 1b.

Next branch was easy (2b), this plant has siliques (long and slender fruits) rather than silicles (more oval fruits).

This is the correct choice, but you are definitely on the wrong road...

Then another easy choice (3b) since the flowers are white rather than yellow (see the quiz for photo with flowers). This is a nice illustration for a morality tale, one wrong turn... Then more trouble.

4a Basal leaves generally hastate (sort of arrowhead shaped), white petals, glabrous (hairless)
4b Basal leaves not hastate, petals often purplish, pubescent



The petals are clearly white, but the basal leaves are also definitely not hastate. There is not a lot of hair on the plant, but there is some. So neither fit exactly, but 4b seems to fit better which would take us to the genus Thelypodium.

The plant is definitely hairy, and the leaves not hastate, definitely not purple though, this is a clue that things are not good.

From the Thelypodium key

The first branch (1b) is easy because the stem leaves are petiolate (have a stalk), the next branch (5b) the plant is biennial (I believe), and I could go with often glabrous though I'm not sure what it means that the siliques are generally spreading to erect.

Fruit with a variable attitude? I don't like glabrous though

But both options of 6 have big problems:

6a Stem 1-6 dm (okay), sepals and petals purple (wrong), siliques 4-7 cm (wrong), ...
6b Stem 3-25 dm (wrong), often hairy (not exactly) petals 6-20mm (nope), ...

That means I had a problem somewhere along the way. Not surprising since I'm still pretty sure I am right about which genus it is (and even confirmed my guess using the much simpler key in Plants of the Pacific Northwest Coast - though it doesn't even list Thelypodium as an option).

After I got this written up I think I figured out the original problem for myself. In the glossary's illustration the stipe is between the receptacle and the fruiting part, rather than between the fruit and the stem as I had been thinking. On closer examination the fruit seems to be sitting directly on the receptacle (is sessile). I will continue from there in the next part of this series.

Nice job figuring out the original problem.