Saturday, February 21, 2009

Isoetes and I

I have always felt that field biologists are primarily explorers. Even as we revel in a new discovery, our minds are already drifting off to the next expedition. We all have our own lengthy lists of locales and taxa for which we pine. For me it is usually a certain species, but with some groups I would be equally happy to find any member of the genus. The genus Isoetes (Isoetaceae) is once such group. With my feet and eyes, I have covered a lot of ground in Missouri and the Midwest. Yet, somehow I have never crossed paths with an Isoetes. I have molested many sterile Eleocharis and Juncus in the distant hope that they were Isoetes. Experience has told me, I will know one when I see one.

Friday morning, I met with the esteemed Missouri Botanist Alan Brant for some stream corridor work in the St. Francois Mountains (center of uplift for the Ozark Plateau characterized by a preponderance of rhyolite). He enticed me along on the trip with the promise of nice weather and possibility of finding some fens, seeps and springs. About a mile into our trek, at the base of a slope, Alan spotted a grove of Alnus serrulata (Smooth Alder) in a young even age cut. Within the grove we could see open grass/sedge areas. Given the geology of where we were and the dominance of Osmunda regalis, Panicum microcarpon, and Alnus serrulata we decided it was an acid seep (really more like an acid fen if such a creature exists). Once we fought our way through the dense stand of saplings and briars that tend to follow blatantly disrespectful logging practices, we explored the seep. As you may know, botanizing in the winter is mostly an exercise in forensics, as the dried and shattered remains of carices, grasses, composites, ferns and the like are the only fodder for study. So anything green, is gold. As I approached some shallow pools that were covered with a thin layer of ice and rife with salamander eggs, I saw green.

Having been prematurely excited on other occasions by what proved only to be Eleocharis stems, I was a bit hesitant to believe that what I was seeing could be an Isoetes. But as I got closer and knowing I had never seen anything so Isoetes-like as these rosettes, my heart jumped. I knew it was my first bona-fide Isoetes. I called Alan over and he verified it.

In Missouri, there are three species of Isoetes, each with a fairly wide distribution (I. butleri, I. engelmannii and I. melanopoda). Two are common and one, I. engelmannii, is listed as “probably state imperiled” (S1?).

While the best way to identify Isoetes englemannii is by the sculpturing on the megaspore, a field determination can be made by habitat, size and characters involving the leaf bases. Isoetes engelmannii is the only submerged aquatic species in the state, as this clearly was; the other two species are more emergent. Isoetes butleri is principally found on calcareous substrates (such as dolomite or limestone glades), so it wasn’t this species. Isoetes engelmannii has pale leaf bases, as did our specimen. Isoetes melanopoda, as the name suggests, has a black coloration to the leaf bases. Thus by morphology and habitat, we came up with the field determination of Isoetes engelmannii. A hard target search of the fen revealed at least 30 more stems. Given the extent of the population and Alan’s opinion that it is far more common than its S1 status indicates (a status more indicative of the rarity of habitat), I collected a small sample. Since it is a new population the sample will be sent to the Missouri Botanical Garden herbarium and an Element of Occurrence Record will be filed with Natural Heritage.

Isoetes (the Quillworts) fit into that silly lay-term “fern allies” that also includes the Horsetails (Phylum Sphenophyta), the Whiskferns (Phylum Psilotophyta) and Club Mosses (Phylum Lycophyta, as is Isoetes)(based on Raven’s “Biology of Plants”, sixth edition). Being an artificial term, “fern allies” has no real taxonomic significance other than designating the non-flowering, non-fern vascular plants. Isoetes is somewhat closely aligned with the Lycopods (Club Mosses) but is the only genus in the order Isoetales. There are roughly 150 known species of Isoetes, distributed worldwide.

Isoetes have a very unique morphology. They grow from a corm which, unlike a bulb (composed of modified leaves), is simply a very short and slightly modified stem. In the photo below the corm is the brown bulbish portion of the base.

The leaves grow from the top of the corm and the roots grow from the bottom. However, Isoetes do it in a strange fashion. The corm is more or less divided into halves. The photo below is taken 90 degrees from the previous photo.

So the corm of Isoetes is kind of like the body of a yo-yo with the leaves and roots growing out along the seam (where the string winds). In the photo below I have made a section perpendicular to the seam.
Here you can see the roots coming out of the heart-shaped bottom of the corm and the leaves out of the heart-shaped top.

The leaves of Isoetes are four-chambered in cross-section. This feature allows the leaves, once gas filled, to float. The base of each leaf flattens out like a clove of garlic. In this “clove” area the sporangia are formed. Like the genus Selaginella, Isoetes are heterosporous (meaning the “male” and “female” spores are very different). The “male” spores are called microspores and the female spores are megaspores. Unlike ferns, the sporangia of Isoetes are like little white eggs. In the photo below (be sure to click on it) you can see last years megaspores (each is about 0.5mm in diameter) erupting from the leaf base. Just to the right you can see some newly formed megaspores.
Each individual plant alternates between the production of male and female spores; the megaspores are produced in the spring and the microspores in the summer. I put several megaspores under the dissecting scope and they are indeed sculpted with ridges which is the key reproductive character for this species in our range.

My mind has been racing, since finding Isoetes engelmannii. I’ve been mentally rearranging my already booked summer schedule for a chance to hunt down the other two species. Where should I look? Perhaps I could cheat by copying label information next time I’m at MoBot. But in reality, plant finds, like many things in life, are best when they are spontaneous. I’m sure I’ll find the other two. And if I’m lucky, it will be when I least expect it.

Tuesday, February 10, 2009

A Quick Guide to Midwestern Andropogon

Whenever one thinks of Tallgrass Prairie grasses, the “big four” often come to mind. The “big four” being Big Bluestem (Andropogon gerardii), Little Bluestem (A. scoparius), Switch Grass (Panicum virgatum) and Indian Grass (Sorghastrum nutans). Though they represent only a fraction of the grass diversity that prairie is capable of expressing, they often make up a significant portion of the vegetative biomass.

All four of these species are easy to identify by their flowering structures and many folks working in prairies can distinguish these species by vegetative (non-floral) means. It is really just a matter of stem bases; Panicum virgatum is the only one with a circular cross section, both A. gerardii and S. nutans have an oval cross section and A. scoparius has a very flat base. Andropogon gerardii and S. nutans can then be separated by ligule length where S. nutans has a prominent and cartilaginous ligule compared to the shorter membranaceous ligule of A. gerardii.

You may have noticed that I refer to Little Bluestem as belonging to the genus Andropogon instead of Schizachyrium. It isn’t that I am stubbornly hanging on to an old name because I fear change and scientific innovation, but rather, because I have read the literature involving the removal Little Bluestem from Andropogon and have found it extremely unconvincing. I’ll address this topic in a future entry.

In the Midwest, A. scoparius is often confused with other flat based members of the genus (basically all but A. gerardii) such as A. virginicus, A. ternarius and A. gyrans (=A. elliotii to some). From my experience, when folks learn to distinguish the similar species, they are surprised at how common the other species are.

In the photo above, you can see all four placed side by side. They are, from left to right, A. virginicus, A. ternarius, A. scoparius and A. gyrans.

Andropogon virginicus (below) is a species of old fields, highway medians and degraded grasslands. It is the most generalist of the group and holds little to no conservation value other than it being better than a field full of exotics. Though I have seen it in relatively intact natural communities, to me it doesn’t seem to have a precise niche in any. Rather, it seems like an ecological anachronism like Gleditsia triacanthos or Maclura pomifera.

To the experienced eye, it is quite distinct even from a distance. It has a more yellow-green cast to the summer foliage and a more yellow-orange cast to the cured stems in the winter (see photo above).
It differs from other Midwestern Andropogon in that the spikelets are included in leaf sheaths and small blades all along the stem (above). Other members of the genus express their spikelets on well exerted peduncles or, as in the case of A. gyrans, the subtending sheaths are large, spathe-like and distributed at the top of the stem. These differences will become more obvious with the descriptions and photos below.

Andropogon gyrans (below) is like a meek, polite and a little fancy version of A. virginicus.

I say this because it occurs in the same weedy habitats as A. virginicus but never in such density. Chances are if you have an abundance of A. virginicus in an area and you look around you will likely find a few stems of A. gyrans mixed in the population. Andropogon gyrans also seems to lack any real fidelity to a well defined natural community or soil type. In fact, all you can say about it and A. virginicus is that they are only found in full sun and moist to dry soils. Andropogon gyrans cures about the same color as A. virginicus but with deeper orange notes along the spathe-like sheaths that subtend the spikelets.

The winter stems of A. gyrans make it the most easily recognized member of the group. The spikelets are more or less congregated in the upper ¼ of the plant and are subtended by the afore mentioned large spathe-like bracts (above). These large bracts give the plant a similar silhouette to that of the tropical genus Heliconia. I have yet to find a consistent field character for distinguishing A. gyrans and A. virginicus without full grown stems. Luckily, one can usually find a remnant stem or two.

Andropogon scoparius (below) is the major player in the Tallgrass and Mixed Grass Prairie systems.

It also contributes significantly to the biomass of glades, woodlands and savannas. The standing, dormant vegetation of A. scoparius is typically more red-orange in color than the yellow-orange of A. virginicus and A. gyrans.
It also differs from A. virginicus and A. gyrans in that its peduncles are not included or otherwise associated with subtending leaf blades or sheaths. Rather, the peduncles are long, exerted and conspicuous (above). When flowering and/or fruiting material are present, A. scoparius can be distinguished from other Andropogon in the presence of a solitary spikelet on each peduncle (A. virginicus, A. gyrans and A. ternarius have two spikelets per peduncle). The best way to differentiate A. scoparius from the other three species in this article is by their ligules. The ligule of A. scoparius is more or less 1 mm long, while the other three have much shorter (less than 1/2mm) ligules. This may seem like a subtle character, but a good field botanist can easily distinguish 1mm from 1/2mm or even 3/4mm. It is all about practice and the perception of scale.

Like A. scoparius, A. ternarius (below) has exerted peduncles.

In fact, they are so exerted in this species that the plants take on a very leggy appearance. This leggy silhouette is further exaggerated by a lack of foliar density, compared to other species. Andropogon ternarius has the red-orange coloration of A. scoparius and is most likely to be misidentified as that species.

The easiest way to tell the two apart, in addition to the peduncle lengths, is that the tips of the peduncles of A. ternarius have a tuft of pubescence (see above and below) whereas A. scoparius is glabrous.
Caution must be used in conjunction with this character because the spikelets of BOTH are pubescent. Of course, A. ternarius has two spikelets (thus the name Splitbeard Bluestem) where A. scoparius has one (seem like a weak character to base a genus on doesn’t it?). Andropogon ternarius has the most southern distribution of the four species mentioned here and is the most conservative. It prefers acidic soils and is less tolerant of disturbance. Where you find it, it is a remnant or relic plant, not a colonizer as the other species mentioned here (less so for A. scoparius, of course). It also makes a nice subject for creative photography.

Lastly, as always, one must keep in mind that this is a diverse group and that along the southern fringe of the lower Midwest one is likely to run into members of the genus not mentioned here; some native, some exotic. That being said, all the other species are different enough that the cautious botanist will instantly know when he/she has stepped outside the comfort zone.