Ημερολόγιο της/του nathanaaron

Hybridity in Dichanthelium is a relatively common yet significantly underreported phenomenon. Hybrids may cryptically appear as true species, especially when isolated from nearby parent entities after being collected for herbaria. This, coupled with the convoluted taxonomic history of the group, plus some members' tendency to be morphologically plastic is probably why hybrids fly under the radar. There are several helpful factors in the matter (these are general behaviors, not strict rules, though):

• True hybrids are almost exclusively sterile. As such, they are reliably found as single individuals in close proximity to the parent entities. (Example 1 Example 2) If you think you have a hybrid, look around! Get a feel for the nearby species. If the unknown entity repeatedly occurs it is likely a true species. If you only find one, plus several other look-alike species nearby, it is likely a hybrid.
• Not only is the hybrid morphology usually precisely intermediate between the parents, the overall form tends to be quite unique and unlike most other true species.
• Hybrid vigor is readily observable in Dichanthelium hybrids. They are usually taller, leafier, and more robust than their parents.
• Plants' ability to hybridize increases after disturbance. Anecdotally, I have found this to be true; I see hybrid Dichantheliums more often in areas that have experienced recent disturbance, like grazing, hot fires, logging, etc.

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Hybrid Form in Missouri Dichanthelium

The most commonly encountered hybrids in Missouri occur as crosses with the linearifolium "grass-like" group (D. linearifolium, D. werneri, D. depauperatum, D. perlongum). These species all form as tufts of mostly basal leaves. Their hybrid offspring will also exhibit similarly long and narrow leaves but their leaves are distributed along the culm and often increase in size distally. For example:

Here is D. linearifolium x boscii, flanked by the parent species. Observation of the hybrid.

Here is D. depauperatum x laxiflorum, flanked by the parent species. Observation of the hybrid.

Clearly the hybrid offspring between a linearifolium group species and a wide-leaved species have a distinctive appearance of long leaves that widely diverge from the stem in dense fascicles. Again, these hybrids are the ones I run into the most, and I suspect they are the most common. As such they are a good gateway into the world of Dichanthelium hybrids.

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Spikelet Intermediacy

Most plant hybrids exhibit intermediate morphology; that is, physical dimensionality that is in-between that of the parents. This is most objectively observable in Dichanthelium by spikelet length. Hybrids almost always have spikelet lengths that are between the parent species. In fact I have never personally witnessed this not be the case, though I'm sure exceptions are out there. Additionally, the shape of the spikelet is often intermediate, though this can be subtle. (The best example of this is D. depauperatum's acute spikelets having clear influence on its hybrid.) Once flowering has begun in spring, most Dichantheliums will have at least a spikelet or two to be found somewhere on the plant throughout the rest of the growing season; verifying intermediate spikelet dimensions is a reliable method in confirming a hybrid. Here are some examples, with links to the observations:

D. scribnerianum x lanuginosum | D. neuranthum x lanuginosum | D. praecocious x perlongum

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Hybrid Denial

As stated previously, hybrids are underreported. I partly blame this on Dichanthelium's troubled taxonomic history (repeated phases of taxa being egregiously lumped and then split), meaning that even today the question of how many true species of Dichanthelium exist is still frequently being asked by even the most knowledgable of experts. For that reason there is a tendency for botanists to assume a strange and distinct looking entity is more likely to be an obscure or as-of-yet undescribed species than a hybrid. It is also likely due to the perceived great difficulty in learning the members of this genus leading many to stop at only a surface level knowledge of the group. Lastly, I do find the hybrids to be unusually common compared to most other plant genera. Perhaps many people simply do not expect hybridity to occur this frequently.

One particularly problematic "member" of Dichanthelium is D. bicknellii.

All Missouri material that I have personally seen/documented that fits squarely within the treatment of D. bicknellii is without a doubt a sterile hybrid between D. ashei and a linearifolium member. I exclusively find this entity in relatively close proximity to the parents, and can vouch that this is the case in all of my iNaturalist observations (Seen here, here, and here). Furthermore, here is an observation by @ciafre in Maryland confirming close parental proximity, and this Ohio observation by @tcurtis even has both D. ashei and D. linearifolium visible in the photo.

Personally, I would like to compare the specimens I collected with the type specimen of D. bicknellii. There may be a true species hidden within the mess, but I have my doubts given the distinctive morphology of distally-increasing leaf lengths, a trait that as I have shown above is typical of linearifolium group hybrids. There may also be species that do not occur in Missouri that look very similar to D. bicknellii and are then mis-ID'd as such. I have little knowledge of such species, though, so I will only speak confidently within the region I'm familiar with.

Another wrench in the cog is the possibility of introgression. A few members of Dichanthelium readily introgress to form locally stable populations of apparently intermediate entities, usually in response to disturbance. (I plan on making another entry going into more detail on this phenomenon along with documentation). It is possible that across the range of D. ashei and D. linearifolium there exists populations of fertile intermediates that have been documented. I personally have encountered a population of D. bicknellii that had frequent individuals scattered about an impacted glade (with both parents present, of course), and the linked observation by @ciafre shows a few growing together as well. Without the personal, hands-on experience with Dichanthelium hybrids and introgressed entities, one would be forced to assume these populations are true species.

This highlights something that makes Dichanthelium both so wonderful and so prone to taxonomic obfuscation: they are incredibly sensitive and adept at adapting to their external environment. The same species can form differently in different growing conditions. Material collected for and studied in herbaria are isolated from the environment from which they grew, and as such the botanist studying them may have lost significant information as to their growing conditions. More obviously, if a hybrid is collected by an unsuspecting collector, they will likely not know to look for and also collect the parents. Quality, important work can be done strictly in an herbarium, but by far the most useful information regarding Dichanthelium requires hands-on, in situ experience.

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If all of this makes the genus sound impossibly cryptic, I assure you the vast majority of the time you will encounter well-behaving, common species in the field. The times you do find tricky, odd-ball hybrid, it is almost always a lone individual imbedded within (or near) populations of frequent species. Fortunately, more and more documentation about these hybrids is becoming available, largely on iNaturalist. The project Hybrid Dichanthelium of North America started by @apbraun1s is a growing repository of such observations.

Here are some of my iNat observations of hybrids thus far:

D. dichotomum x linearifolium
D. dichotomum x laxiflorum
D. werneri x sphaerocarpon
D. werneri x boscii
D. werneri x ashei
D. linearifolium x ashei
D. linearifolium x boscii
D. linearifolium x lanuginosum (putative)
D. depauperatum x laxiflorum
D. perlongum x praecocious
D. scribnerianum x lanuginosum

Arguably the most well known character uniting the genus Dichanthelium is their twice[1]-flowering behavior, as each species exhibits markedly shifting morphology throughout the growing season. Though exact timing and growth pattern varies from species to species, they tend to flower first in the late spring/early summer and again in mid-late summer. The primary (vernal) spikelets are born on a terminal panicle (a branching inflorescence, like this ) reminiscent of the closely related genus Panicum. As the season progresses the plants branch from the axils of the stem (at the bases of leaf sheaths) and produce secondary branches and panicles. (While we refer to the second flowering as autumnal, it's important to know that this almost always happens in mid-late summer.) Additionally, many species will also produce autumnal spikelets hidden to varying degrees within the leaf sheaths, and this usually happens by late summer to early fall.

The vernal flowers tend to be numerous and chasmogamous (open, thus cross pollinating) while the autumnal flowers tend to be few and cleistogamous (closed, thus self pollinating). There is variation between species in the autumnal form; some species create readily apparent axillary branches bearing secondary leaves, while others create dense fascicles of secondary leaves sprouting from the gap between the primary leaf sheaths and the stem. It's also important to note that the branching that begins in the summer is more or less an ongoing process that continues until the end of the growing season.

The flowering, branching, then flowering again behavior is important to grasp if one wants to familiarize themselves with this genus. It's no complicated process, but it does mean the overall appearance (gestalt) of many Dichantheliums can exist in multiple forms depending on seasonality. Here are some examples:

(The photos are not clickable, but zooming into the page works well as the photos as displayed are full size. If you still want better access to a photo, right click and click "Open Image in New Tab".)

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Branching

Dichanthelium scoparium as it appears in early and late summer. It is a tall, robust grass and is exemplary of Dichantheliums that form secondary branches. Note that at the tips of these secondary branches the leaves reduce in size and appear to cup the secondary spikelets (which are mostly hidden from view).

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Fascicled

Dichanthelium lanuginosum in spring and mid-summer, with detail on the secondary spikelets. The secondary branches are very short, giving a "fascicled" appearance. This species is variable in its autumnal form depending on location, see its species page for more information.

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Loosely Fascicled

Dichanthelium ashei in spring, summer, and fall. In summer, the secondary branches and leaves (which are of similar proportions to the primary growth) have fully emerged giving the plant a full appearance. Notice that in the summer photo the primary inflorescences are bare as the spikelets have detached. By fall, the primary growth has withered away, leaving the clustered secondary growth towards the tips of the stems.

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Grass-Like

Dichanthelium linearifolium in spring, late summer, and winter. Most of the tufted "grass like" Dichantheliums follow very similar morphologies: tall panicles in the spring followed by completely (or nearly so) sessile inflorescences in the bases of the leaves in mid-late summer. In some species the secondary spikelets are fairly observable, for others one may need to peel open sheaths to see them. During the winter, most signs of the previous spring's growth are gone while much of the autumnal leaves may stay somewhat green.

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As previously mentioned each species varies in the degree to which they branch, however the vast majority will appear similar to one of the examples listed above. The shifting morphology highlights the importance of spikelet and ligule measurements for identification as these characters remain consistent no matter the time of year. That being said this primarily a visual guide, so I will still be focusing more on characters related to overall appearance.

[1] Per LeBlond, the genus can also be considered to be thrice-flowering, as the cleistogamous inside-the-sheath spikes usually flower after the secondary flowers. I agree with this observation, but for the simplicity of this guide I will still be referring to vernal and autumnal flowering stages.

Click here for a visual overview on the twice-flowering morphology of Dichanthelium.

Click here for information and documentation of Dichanthelium hybrids.

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This post serves as an introductory 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! It should be noted that this guide is not strictly exhaustive for Missouri Dichanthelium; there are a few species that are much more rare, only known from historical collections, or whose existence here is questionable. For the sake of brevity I have omitted those for now (but they may be added in later).

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 in part 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.

Dichanthelium you will see very regularly:

• D. boscii - woodlands
• D. clandestinum - sunny riparian generalist
• D. dichotomum - acidic woodlands
• D. lanuginosum - woodlands, grasslands, old fields, disturbed ground
• D. linearifolium - open woodlands and glades
• D. malacophyllum - edges of grasslands, old fields, trails, roads, urban areas
• D. sphaerocarpon - rocky soil of grasslands, woodlands, and glades
• D. scribnerianum - woodlands, grasslands, old fields, disturbed ground

Dichanthelium you will see somewhat regularly:

• D. ashei - dry acidic woodlands
• D. depauperatum - calcareous glades and open woodlands
• D. laxiflorum - acidic woodlands and edges of glades
• D. longiligulatum - periphery of ponded wetlands, banks of streams, wet prairies
• D. polyanthes (Eastern Missouri) - acidic, rocky soils, from glades to edges of streams
• D. scoparium - sunny wet grasslands and old fields
• D. werneri - dry acidic woodlands

Dichanthelium you will see infrequently:

• D. commutatum - dry acidic woodlands
• D. implicatum - dry acidic woodlands, sandstone exposures
• D. latifolium - mesic, shaded riparian edges and forests
• D. microcarpon (Eastern Missouri) - acidic wetland soils
• D. oligosanthes (Southern Missouri) - sandy, shaded woodlands, sandstone glades
• D. perlongum - remnant prairies and glades
• D. ravenellii (Southern Missouri) - dry acidic woodlands
• D. praecocious - exclusive to remnant prairies
• D. villosissimum - acidic woodlands

Dichanthelium you will see uncommonly:

• D. columbianum (Southeastern Missouri) - sand prairies
• D. inflatum (Southern Missouri) - sandy/acidic edges of woodlands
• D. leibergii - remnant prairies and glades
• D. neuranthum (Southwestern Missouri) - remnant prairies

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

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 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

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, has smaller spikelets, 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. I most frequently come across it in and around calcareous glades and open woodlands. Famously recognized by its "dunce cap" pointed spikelets. The upper leaf surface is only sparsely hairy and terminates at a very short ligule, 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 lower 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 belonging to the D. acuminatum complex. 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, especially acidic woodlands. Check for small spikelets, hairy leaves, and sheath hairs that are equal or less than the sheath width (rarely slightly longer).
The synonym for this species when it is retained within the concept of D. acuminatum is D. acuminatum var. fasciculatum. Don't be surprised if the key you're using doesn't use D. lanuginosum, it is still widely considered to be a variety.
There is a common entity found along calcareous rocky banks of streams and creeks that technically falls under our concept of D. lanuginosum, and it looks like this. It is very similar to D. lanuginosum but with glabrous leaves. It is not certain whether this is separate species or merely a form of D. lanuginosum.
See here for a comparison with D. malacophyllum.

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. I find that the leaves clasp much more strongly, as well.

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 with pustular bases 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. 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. Furthermore, it is often the tallest and leggiest grass-like Dichanthelium. Individuals on acidic glades, for example, can attain quite the stature.

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. This grass is increasing in distribution; I find it even around pasture ponds.

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).
See here for a comparison with D. lanuginosum.

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 shorter and are distributed along the stem and not growing basally; the plant is usually quite glabrous.

Dichanthelium oligosanthes

Uncommon in Missouri, known from scattered locations in the southern and eastern Ozarks (though it is probably overlooked). Appears like the very common scribnerianum but with narrower, longer leaves, a longer ligule, and bigger spikelets. The leaves are often widely spreading, compared to scribnerianum's more ascending leaves. Look for this species in sandy soils, like sand prairies, sandstone glades/woodlands/etc.

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) rounded 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, see here for a comparison between the two.

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. Also, the leaves (especially towards the later end of the season) tend to be strongly ascending, further separating it from D. lanuginosum's more spreading leaves.

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. The upper leaf surface is glabrous, the lower is hairy.

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; the ligule is absent or minuscule; and the leaves are thick, erect, and with prominent marginal cilia towards the base. See here for a comparison with *D. polyanthes.

Dichanthelium scribernianum

Very 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 leaves are glabrous on the upper surface and often "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.