November 01, 2023

Visual Guide to Dichantheliums in Missouri

This post serves as a (hopefully) useful Dichanthelium guide by being a repository of diagnostic photos and characters for each species. This plant genus is the second-largest in Missouri and can appear quite daunting; that being said, due to the broad range of morphologies represented in this group, learning the different entities can be quite easy when you experience them visually (especially in person, of course) with a firm emphasis on habitat. Most species are fairly restricted to very predictable habitats, after all, so you don't need to rely on checking against every other Dichanthelium when you're looking for an ID.

Keys published for groups such as this one are usually technical, relying on spikelet size and ligule length (often in the sub-milimeter range) which can add to the reputation as being "too difficult". However, it is important to note that many keys are written using herbarium material and as such are typically used to identify herbarium specimens, and not necessarily plants in situ. It can be easy to fool yourself into thinking that the morphological characters used in keys are the only visually identifiable features that can be used to tell two species apart, when in reality these characters are usually the ones that are most objective, repeatable, and more apparent in pressed specimens. Thankfully, living plants in situ are bursting with unique character and as such a visual field guide such as this one should hopefully make quick sense. Seeing as how this is an ongoing work in progress, please feel free to add feedback or things you feel need corrected!

Much credit goes to Justin Thomas whose decades of experience with these grasses has been a key part of my (and many others') journey into understanding them. In particular, the D. acuminatum group for many years was considered one species containing a plethora of obscure entities, but due to his research and experience is now well understood to be at least 10 distinct species. See: REVISION OF DICHANTHELIUM SECT. LANUGINOSA (POACEAE)

Spikelet dimensions and botanical illustrations borrowed from Flora of North America.

Most photos are mine; if not, links to the original observation are provided

Dichanthelium ashei

Characteristic species of chert and sandstone woodlands, with a low stature, mostly glabrous sheaths, and blue-green hue. The leaves are usually clustered towards the tip of the stem, especially towards the latter half of the season.

Dichanthelium boscii

(Observations for photos 1 and 2)
Very common species of dry forests and woodlands throughout the state. Look for the large spikelets, conspicuously bearded nodes, and lack of basal leaves. It is usually the largest woodland Dichanthelium.

Dichanthelium clandestinum

(Observations for photos 1, 2, and 3)
Very common grass throughout its range where it can be found in wet, open sites, especially along creeks and rivers, usually in abundance where regular disturbance occurs. It is the largest Dichanthelium in the region and is recognized by its wide leaves and stem; large, stiff hairs on the sheath with pustular bases that are nearly sharp to the touch; and habitat.

Dichanthelium columbianum

This is a grass that is endemic to sand and dune communities. As such, it only grows in the few sand prairies that occur in Missouri in the bootheel region. It is a characteristic species for said communities and is unusual for hairy Missouri Dichantheliums by lacking hair along the center of the adaxial leaf surface.

Dichanthelium commutatum var. commutatum

(Observations for photo 3)
A dry woodland (usually acidic) species that is not very common in Missouri (though it is not rare). Looks very much like D. boscii but lacks long hairs on the nodes, is slightly smaller, and retains conspicuous basal leaves.

Dichanthelium depauperatum

One of the four Dichantheliums in the area with long, "grass-like" leaves, found in grassland or woodland communities, usually over acidic soil (though I do come across it in and around calcareous glades). Famously recognized by its "dunce cap" pointed spikelets. The upper leaf surface is only sparsely hairy, a trait it shares with its closest lookalike D. werneri.

Dichanthelium dichotomum

Common species of dry open forests, woodlands, and other similarly semi-open and dry sites Thin, short leaves; branches diffusely; tiny spikelets; often with a disproportionately tall vernal inflorescence. Also, the nodes are usually retrorsely hairy. Can be confused with D. microcarpon, though that species grows in wetter sites and has reliably smaller spikelets (around 1.6mm, compared to around 2.0mm)

Dichanthelium implicatum

Uncommon member of high quality woodlands and grasslands, usually of acidic substrates. In Missouri it is most likely encountered in cherty woodlands or around sandstone exporures. Morphologically between lanuginosum and villosissimum; long, erect hairs on adaxial leaf surfaces; small spikelets; sheath hairs that are not much longer than sheath width. Very ubiquitously, in the dormant season the autumnal leaves become distinctly recurved (see photo).

Dichanthelium inflatum

This coastal plain species is similar in appearance to the widespread D. sphaerocarpon but is restricted to extreme southern Missouri where it is found on sandy, acidic soils. Its leaves are narrower with mostly parallel margins and has fewer marginal cilia (long hairs) towards the leaf base.

Dichanthelium lanuginosum

A widely distributed and morphologically variably species. Usually found in open, grassy places, like woodlands, glades, prairies, sometimes edges of lawns, old fields, etc. It is more common in impacted/disturbed communities but can still be found in high-quality sites. Check for small spikelets and sheath hairs that are equal or less than the sheath width (rarely slightly longer).

Dichanthelium latifolium

A less common species of mesic forests and riparian corridors of at least some remnant quality. Can be a dead-ringer for clandestinum but is easily differentiated by sheaths that are completely glabrous minus a line of hairs along the margins, along with being overall slightly smaller in stature.

Dichanthelium laxiflorum

One of the more unique and easily recognizable in the genus and is commonly encountered in woodlands across the Missouri Ozarks. Owing to the name, it is quite prostrate and "floppy"; tufts sprouting long lime-green hairy leaves with marginal cilia halfway up the length. Usually grows in colonies.

Dichanthelium leibergii

A distinct grass of high quality prairie and glade remnants that is rare in Missouri. Large for a grassland Dichanthelium, it is evenly covered in short, erect hairs and has a "fuzzy" appearance. Also look for spikelets with long hairs and a very short ligule.

Dichanthelium linearifolium

One of the four Dichantheliums in the area with long, "grass-like" leaves, found in grassland or woodland communities (especially glades). Of the four it is typically the hairiest, with conspicuous, messy, long sheath hairs of varying lengths. Additionally the upper leaf surface is also consistently short hairy (making the ligule difficult to isolate visually), a character that separates it from D. depauperatum and D. werneri.

Dichanthelium longiligulatum

A somewhat cryptic, short-leaved species that favors acidic soils near wetlands, like natural ponds or creeks. Owing to its name it has a very long, distinct ligule. Also look for very small spikelets (around 1.0mm), few to none marginal cilia, and leaves that are consistently short. By the autumnal phase it usually takes a pom-pom like appearance with orderly fascicles of leaves occurring along the stem.

Dichanthelium malacophyllum

A Dichanthelium that can be readily ID'd with just a single touch of the thin leaves as this species is covered in very short, soft hairs that feel like felt. It is somewhat common in the southern half of the state, though it is probably overlooked. Usually found in dry, disturbed sites like old fields, edges of lawns, and edges of glades. Tends to grow a little taller and leafier than other Dichantheliums with similar leaf proportions. Sometimes D. lanuginosum can appear similar to malacophyllum, but its spikelets are nearly half as long, appearing distinctly smaller (approx. 1.5mm and 3.0mm, respectively).

Dichanthelium microcarpon

A grass that is much more common further east but is more restricted in Missouri as it prefers acidic, wet, rocky substrates. Here it is most commonly found in the St. Francois Mountains region along creeks, seeps, and streams, less commonly around sinkhole ponds and low wet areas in prairies. The stems become highly branched through the season and bear small spikelets and nodes with distinctly retrorse hairs.

Dichanthelium neuranthum

A coastal plain species that is rare in Missouri, found in just a handful of prairie remnants in the southwestern and western portions of the state. Where it does occur here, though, it is often in abundance and is probably overlooked. The leaves are as thin or even thinner than the "grass-like" species but are distributed along the stem and not growing basally; the plant is usually quite glabrous.

Dichanthelium oligosanthes var. oligosanthes

Very rare in Missouri and is only known from a few southern locations (though is potentially overlooked). Looks like the very common scribnerianum but with narrower, shorter leaves, a longer ligule, and is typically darker green. The above photos are from a sand prairie in the bootheel region.

Dichanthelium perlongum

(Observation to photo 2)
The most uncommon of the four "grass-like" species, being found only in high quality prairies, glades, and sometimes open woodlands. Look for large (<3.0mm) spikelets born sparsely on the inflorescence and abaxial (lower) leaf surfaces with dense, orderly, ascending hairs.

Dichanthelium polyanthes

Another species that is much more common further east and is found near the edge of its range in eastern Missouri where it is often encountered in woodlands of varying substrates (though usually acidic). It is a tall Dichanthelium with wide leaves and large, conspicuous inflorescences that are taller than wide and adorned with small, round spikelets. The big brother of D. sphaerocarpon.

Dichanthelium praecocious

A relatively sensitive species of high quality tallgrass prairie remnants than can become locally extirpated given enough disturbance. It looks very similar to lanuginosum, who it often co-occurs with, but faithfully bears sheath hairs that are much longer than the sheath width. Towards the end of the summer the leaf and sheath hairs become scraggly, stiff, and disheveled, feeling very different from other grassland Dichantheliums.

Dichanthelium ravenellii

A slightly uncommon grass of high quality acidic woodlands in the southern third of the state. It is unusual in appearance, with long, curled-upward leaves clustered towards the tip of the stem (appearing fascicled) and very large, hairy spikelets.

Dichanthelium scoparium

A fuzzy Dichanthelium found in open, often wet ground in southern Missouri. It's a characteristic species of prairie swales but can be found in a variety of other habitats. It usually grows quite tall with short autumnal branches. The numerous felty, arching leaves are distinctive, but the best character is the stem pubescence that increases in density above each node, followed by a "bald patch" beneath the node.

Dichanthelium sphaerocarpon

One of the more common species in the state, occurring in a variety of dry habitats, usually on rocky soil. It is often smaller than most others in the group, and is known for the orbicular spikelets for which it is named. The sheaths are glabrous, and the leaves are thick, erect, and with prominent marginal cilia towards the base.

Dichanthelium scribernianum

Extremely common, weedy species found throughout the state. It is most commonly found in overgrown lawns, fields, roadsides, etc., though it is regularly found in more intact communities like prairies, glades, and openings of woodlands. The glabrous leaves are long and "boat shaped" as the tips curve upwards, the sheaths are stiff-hairy with pustular bases, and the spikelets are large (in the 3.0mm range).

Dichanthelium villosissimum

Characteristic species of high quality chert/sandstone woodlands in the southern third of Missouri. It puts the villous in villosissimum! It is well adorned with long, wiry hairs that are exceedingly longer than the sheaths are wide. It is often prostrate and messy in posture later in the growing season. Most similar to D. praecocious but their habitats almost never overlap.

Dichanthelium werneri

One of the four Dichantheliums in the area with long, "grass-like" leaves and a characteristic species of acidic woodlands. Very similar in appearance to depauperatum, but with more blunt spikelets (not dunce-cap shaped) and often with slightly revolute leaf margins that, when added with the slightly recessed central vein, lead to a subtle "m" shape to the leaf cross-section.

Posted on November 01, 2023 02:59 AM by nathanaaron nathanaaron | 6 comments | Leave a comment