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"Will the Real Trillium sessile" Please Stand Up?"

Moving to the USA in 1995 onto a property with over 1.5 acres of deciduous woodland provided the perfect opportunity to expand an interest in trilliums, particularly those of the south-eastern states which form the subject of this photo-essay.

All trilliums can be conveniently described as either sessile or pedicellate, i.e. the flower either sits directly on top of the leaves (sessile, subgenus Phyllantherum) or has a pedicel (pedicellate, subgenus Trillium).  In the latter, the flower may be erect or held below the leaves.  The sessile and pedicellate trilliums are dissimilar in a number of ways pertaining to the leaf form and coloring, and especially the flower structure.  Both groups are indispensable elements of the woodland flora, providing superbly attractive foliage and flowers over several months in the spring, the sessiles generally flowering earlier than the pedicellates, often starting in late February or early March, depending upon location.

Filled with enthusiasm but initially skeptical that the delineation of many of the described species were justified, after over 25,000 miles of travel in the Deep South I think I can safely identify all of the accepted sessile-flowered species.  Excitingly, at least a couple of populations of sessile trilliums that I have come across on my travels defy identification, even in the eyes of the confirmed ‘lumper’.  However, the pedicellate members of the ‘erectum complex’ (T. cernuum, erectum, flexipes, rugelii, simile, sulcatum & vaseyi) seem to be an unholy mess, defying definitive identification in any other than their purest forms.  Trillium pusillum is easily recognized but suffers from a plethora of varieties most of which are doubtfully distinguishable – at least in the absence of a DNA sequencer.  Trillium catesbaei and nivale are well behaved and understand their role in the bigger picture.

Given these issues, and the fact that a number of the sessile species are barely in cultivation, it is understandable that many trilliums are misidentified in cultivation.  I hope this article goes some way towards clarifying the identity of members of this uniquely beautiful group of plants as well as highlighting some of the special forms that can be found. 

Sessile Trilliums - subgenus Phyllantherum

T. decipiens, reliquum & underwoodii
With much in common, these three species should be grown for their stunningly beautiful leaves alone, blotched in every shade of green overlaid with streaks of cream and silver.  The leaf markings remain fresh and bright from unfurling to dormancy, in sharp contrast to leaves of species such as T. cuneatum which rapidly fade to muted greens and browns.  Their flowers are also very similar, being erect and generally colored from a dark brown-maroon to a rich red-maroon, although yellow-green forms can occasionally be found.  As is the case with flowers of all sessile species, the colors fade with time but they are exceptionally long-lived.  The major difference between them is one of stature of flowering plants, and the ratio of leaf length to stem height.  In T. underwoodii the stems are 3” to 8” tall and 1 to 1.5 times the leaf length, whereas in T. decipiens the stem height is 15” to 18” and the ratio increases to over 3, the leaf size remaining similar.  T. underwoodii from Alabama are much better garden plants than those from the Florida panhandle, the latter like to rise in late January!  T. reliquum is an almost decumbent plant, the leaves sitting on or just above the forest floor.  It is quite different from T. decumbens in a number of features, particularly its non-pubescent stem.  An S-curve in the stem is quoted as being diagnostic but this character is not reliable. Now to the problem - it is effectively impossible to distinguish between non-flowering plants of T. decipiens, reliquum and underwoodii

T. decumbens
This gorgeous decumbent species has a diagnostic pubescent stem and is impossible to confuse with any other trillium.  The leaves are generally two-tone, green and pewter, with none of the ‘camouflage’ markings of T. underwoodii; open flowers are a glossy red-maroon and the petals are attractively twisted at the tips.  The degree of silvering of the leaves and the arrangement of the markings can be very variable, some forms with pure silver leaves can be found, but there is negligible variation in the flower color.

T. maculatum
The ‘maculatum' refers to the leaves, which can be strongly and darkly mottled.  The flowers are tall, elegant and a clear red-maroon, lacking the brown overtones that flowers of many sessile species can have.  The petal shape distinguishes this species from others superficially similar such as T. cuneatum.  Pure lemon-yellow forms exist, and if you are incredibly lucky you might find T. maculatum f. simulans with yellow and maroon bicolored petals. 

T. cuneatum & luteum
T. cuneatum is easily the largest of any eastern sessile trillium, and can be rather coarse but it is particularly spectacular when seen en masse.   Petal color varies from yellow through green to brown and deep maroon; leaves can be pure silver, green or strongly mottled.It is most similar to T. luteum, whichis a large relatively invariant yellow, flowered species which is easily recognized.   

T. foetidissimum, gracile & ludovicianum
T. foetidissimum is relatively invariant in flower and leaf, although pure yellow forms can very occasionally be found.  It seems to be more predisposed then most to throw forms with all-over silver leaves.  In size and proportion it is similar to T. discolor and quite charming.  With dark red-maroon flowers, it has strongly mottled leaves and is true to name, the flowers emitting a fetid odor.  It is the first to emerge in mid-March and can be damaged by late winter freezes.  However, plants in more sheltered spots were fine.  T. ludovicianum and T. gracile definitely fall into the category of hard to distinguish between if you don't know their origin!  T. ludovicianum complicates matters because it can co-exist with T. cuneatum with which it may intergrade. T. gracile & ludovicianum have a range of petal colors similar to that of T. cuneatum and the leaves are very attractively mottled; the plants are generally much smaller and more refined.  T. gracile flowers in the wild in April, whereas T. ludovicianum and T. foetidissimum arein full flower in the first week of March.  T. gracile is the last sessile species to flower in SE Pennsylvania.

T. discolor
In comparison with the other normally yellow sessile trillium, T. luteum, this is a truly refined species and quite distinct.  Although generally dwarfer in all proportions than T. luteum, very robust individuals can be found.  Unlike the acid yellow of T. luteum, the petals of T. discolor are a soft creamy to a deeper yellow and upon seeing large colonies of them, the effect is one of seeing thousands of candles.  The petal shape is uniquely spatulate, much broader at the tip than the base, and the stamens are purple. They are delightfully fragrant of lemons and particularly nice forms may have strong red flares extending up from the base of the petals.  The leaves can be nicely marked but fade quickly.

T. sessile
T. sessile is most frequently misrepresented in cultivation; most of the plants bought or seen under actually correspond to T. cuneatum or one of the western sessiles, although the true plant is of much smaller stature than any of these.  It can be a charming plant and very fine forms with excellent leaf mottling and petal color can be found.  In particular, I have seen yellow plants, and those with yellow flowers edged with purple, creating a very attractive picotee effect.

T. viride & viridescens
T. viride and T. viridescens are both large, green flowered plants, sometimes with a purple base to the petals in the latter case and are frequently confused in cultivation.  The leaf markings fade rapidly and are not particularly showy. 

T. lancifolium, recurvatum & stamineum
Although these three species are related they are very easily distinguished from each other and from other species.  None can be described as showy but each makes a unique contribution.  They are also interesting because they have a natural propensity to form clumps, something that most trilliums will not normally do. T. stamineum is a medium sized species with small flowers, the fragrance of which can be rather unpleasant.  However, the thin dark maroon petals are horizontally inclined and uniquely twisted along their length. T. lancifolium also has twisted petals in many forms, but these are long, thin and erect.  It also has a unique look, taking its name from the lance-shaped leaves (which can in reality be much broader than lance-shaped).  The stems can easily be up to 18” tall.  Flower color is variable, from dark red-maroon, through bicolors to almost green.  The rhizome is also unusual, being long and thin, and very brittle.  It tends to form tight clumps more frequently than most other trilliums.  T. recurvatum is also easily identified with its petiolate leaves, recurved sepals and relatively short petals.  It normally has a brownish-maroon to red-maroon flower and can be quite variable in size, petal color and leaf marking.  Plants with all-over silver leaves can be seen and T. recurvatum f. shayi is a yellow flowered form.

Pedicellate Trilliums - subgenus Trillium

T. catesbaei
T. catesbaei is an exceptionally classy plant with distinctly petiolate plain green leaves, as is the case for all of the eastern pedicellate species.  The flower is generally held below the leaves and is quite variable in size.  The petals can be white to a stunning deep rose pink. 

T. erectum complex (cernuum, erectum, flexipes, rugelii, sulcatum & vaseyi)
This is the section that could get me into real trouble!  I'm probably on safe ground starting with the descriptions of the ‘pure’ plants, but you'll soon get the message that you may have more chance of winning the lottery than correctly identifying your pedicellate trillium from this group.  All of the species have large plain green leaves.  T. cernuum has white, strongly recurved petals in a flower held tightly below the leaves and its habit of hiding its flowers beneath a large leafy canopy makes it not particularly showy. The stamens and ovary of T. cernuum are white whereas the anthers of T. rugelii are purple and the ovary is purple-streaked or maroon.  The flowers of T. rugelii can be much larger than those of T. cernuumT. erectum  can be anything from 8 – 24” tall, with flowers, flat and wide-spreading in profile, of white, red, maroon, yellow-green or red-brown, the petals frequently tending to be lanceolate in shape.  The flowers can be erect, straight out sideways or declining.  T. flexipes is usually 15 – 18” tall, traditionally white flowered with broader petals on erect flowers with a creamy-white ovary.  Quite where T. flexipes begins and ends is a mystery because forms with every ovary color imaginable can be found and it becomes impossible to tell what is a white T. sulcatum, T. erectum f. album or T. simile.  The latteris a very attractive large species, often forming clumps, with erect creamy-white flowers with a purple ovary.  The overall impression of the flower is of a candle snuffer - broadly funnel-shaped with the ends of the petals flaring sideways.  However, apart from the flower shape of this ‘classical’ form, it is no different to T. erectum f. album.  T. sulcatum is of similar stature and equally showy but has dark red-maroon to purple flowers with sulcate sepals and broad petals that are slightly flatter than those of T. simile.  Occasional white, pink, cream and yellow forms can be found together with beautiful bicolors and picotees.  Last but not least is T. vaseyi, a spectacular species with huge (up to 3” across) flowers of deep red-maroon nodding below the leaves.  White flowered forms are known and it is the last species to flower in SE Pennsylvania.   All of these subjects make superb garden specimens and it is important not to get too hung up on nomenclature. 

T. nivale
The Snow Trillium is by far the earliest flowering trillium here in early to mid-March, long before most trilliums are even through the ground.  The flowers are pure white to creamy-white, of heavy texture and prominently veined, and replete with beautiful golden yellow anthers.  Although its leaves are unmarked, the best forms are a wonderful shade of blue-green, overlaid with a pewter caste, and often with the veins picked out with silver speckles.

T. pusillum
T. pusillum is a beautiful species but a rather confused little fellow, or at least it has managed to confuse a large number of botanists.  There are currently 6 or 7 published varieties, but the distinctions between many are blurred.  Suffice to say it is always very charming, dwarf (3” – 12”) and has an upwards facing white flower.  The flower often has ruffled margins and, in the manner of Trillium grandiflorum, fades to rose pink as it ages.  The foliage of some forms is almost purple in color until it matures to a deeper green. 

Of the eastern pedicellate species, only T. grandiflorum, persistens and T. undulatum have not been included.  T. grandiflorumis universally grown and well understood, T. persistens is federally endangered and the least showy of all the pedicellate species, and T. undulatum is instantly recognizable but sadly the most difficult trillium to grow outside of its native range.

This article is not intended to cover aspects such as the distribution, cultivation or propagation of trilliums, much more about which can be found in the two excellent books referenced below.    I hope it encourages members to try more trilliums and better understand those they are currently growing. 

Many more pictures of all of these species and forms can be found on my web site at:

Trilliums by F.W. and R.B. Case (1997). Timber Press, Portland, Oregon, USA.

Trilliums in Woodland and Garden -  American Treasures.  D.L & R.L. Jacobs.  Eco-Gardens, Decatur, Georgia, USA