Explore Plants by Form

 

On This Page:

• Trees
• Shrubs and Dwarf Shrubs
• Forbs
• Ferns and Fern Allies
• Grasses, Sedges, and Rushes
• Mosses and Liverworts
• Lichens

Select a category below to learn more about the ecological role of these growth forms and browse highlighted species.

Trees

Trees are single-stemmed, woody plants that are generally taller than 10 m (~30 ft) when mature. In the boreal forest, trees are often stunted and dwarfed.

Trees tend to thrive where there is sufficient warmth and nutrients. In these areas, trees are able to grow taller than their neighbors and can therefore capture more sunlight, shading and out-competing their neighbors. However, because trees must invest a lot of energy into building the structural tissues (wood) that will give them this competitive advantage for light, they are sometimes at a disadvantage where resources (such as nutrients and radiation) are very limited. In these “stressful” environments, plants whose bodies are constructed to take maximum advantage of the limited light, radiation, and nutrients that are available are favored by evolution. This often means not investing in energetically “expensive” structural tissues such as wood. Most low-growing, non-woody plants have a higher percentage of their bodies directly devoted to photosynthesis and uptake of nutrients, and thus can be more “efficient” in more stressful growing environments with short, cold growing seasons.

 

 

NPS Photo

You can observe the results of this dynamic competition between different kinds of plants very clearly on the landscape of Denali. Trees tend to grow best in the lowlands where it is warmer and sunnier and along rivers where the flowing water has melted the permanently frozen ground. In fact, trees dominate the landscape in many lowland areas of the Park. Forests blanket the river plains and lower hills in the Park where the growing season is longer and warmer, and conditions are more favorable for plant growth. As you start to climb out of the valleys up to the ridges where it’s often cold and windy, you will notice that trees (and even lower shrubs) become fewer and farther apart, and the vegetation is lower to the ground with fewer woody species and many more grasses and forbs.

Denali is situated north of sixty-one degrees north latitude. Because of this, there are only a handful of tree species that are able to grow and reproduce naturally this far north. In fact, if you go a few hundred kilometers even further to the north, you will reach the arctic tundra biome, where there are virtually no trees at all. There are only eight species of trees that occur in Denali National Park and Preserve. Three of these are coniferous (cone-producing) plants from the pine family (white spruce, black spruce, and larch) and the other five are flowering plants from the willow and birch plant families (quaking aspen, balsam poplar, black cottonwood, Kenai birch and Alaska birch). Also note that there are some tall shrubs, primarily willows and alders, which could be mistaken for trees.

Pine Family

• Picea glauca – white spruce
• Picea mariana – black spruce
• Larix laricina – larch

Willow Family

• Populus tremuloides – quaking aspen
• Populus balsamifera – balsam poplar
• Populus trichocarpa – black cottonwood

Birch Family

• Betula kenaica – Kenai birch
• Betula neoalaskana – Alaska birch

 

Hikers make their way through dwarf birch and other shrubs.

NPS Photo / K. Karnes

Shrubs and Dwarf Shrubs

Shrubs are woody plants that are less than 10 m tall when mature, and are usually multi-stemmed. In the boreal forest shrubs are often less than 3 m tall (~10 ft) tall, but some willows can attain tree-like heights of greater than 5 m. Dwarf shrubs are woody plants that are less than 30 cm (~1 ft) tall and characteristic of the alpine tundra blanketing the ridges and slopes of Denali above approximately 3500 feet (1066 m) in elevation.

Shrubs

Shrubs are very abundant in Denali, including many of the areas often frequented by visitors along the park road. Shrubs are absent from only the highest alpine areas and some of the very wettest wetland plant communities. Shrubs tend to occur most abundantly in subalpine regions where trees are less common, in riparian areas along streams, (where many species of willows and alders like to grow). Shrubs are also common in the understory of some of the boreal forest types in the park. There are a few species of shrubs that occur above treeline, even at elevations up to 1500 m (5000 ft).

There is a much higher diversity of shrub species in Denali compared to trees. There are 52 species of shrubs representing 10 different plant families that occur in Denali National Park and Preserve. The willow (Salicaceae) and heath (Ericaceae) families contribute the most species of shrubs to our flora, with 17 and 11 species respectively. Other plant families that are represented by shrubs in our flora are the Rose (Rosaceae), Birch (Betulaceae), Currant (Grossulariaceae), Honeysuckle (Caprifoliaceae), Dogwood (Cornaceae), Oleaster (Elaeagnaceae), Cypress (Cupressaceae), and Bayberry (Myricaeae) families.

Dwarf Shrubs

Dwarf shrubs are hardy perennials are the dominant component of many tundra types found in the park, particularly in some areas of late-lying snow in saddles and protected slopes. Mountain Avens (Dryas spp.) tundra is perhaps the most familiar and welcome vegetation type to hikers in the Alaska Range, because it is very common and it usually affords solid footing, dry feet and fast traveling. A surprise for many of our visitors from the south is the dwarf willow shrubs that adorn the mountains of Alaska. These diminutive tundra-dwellers that reach just a few centimeters in height are in fact very close relatives (in the same botanical genus – Salix) of the familiar “weeping willow” tree (Salix babylonica).

There are twenty-six species of dwarf shrubs that occur in Denali National Park and Preserve representing five different flowering plant families:

• Heath family (Ericaceae, 11 species)
• Willow family (Salicaceae, 7 species)
• Rose family (Rosaceae, 5 species)
• Crowberry family (Empetraceae, 1 species)
• Diapensia family (Diapensiaceae, 1 species)

 

Fireweed blooming in mid-summer.

NPS Photo / Damian Popovic

Forbs

Forbs are herbaceous flowering plant species. This category includes those plant species people think of as “wildflowers” such as goldenrod, gentian, fireweed, forget-me-not, larkspur, lupine, monkshood, poppies, and violets. This is the most species-rich group of plants in the Denali National Park and Preserve flora, including over 450 species from 54 families of flowering plants.

Forbs occur in all habitats across the park from aquatic communities to the driest, most windswept scree-slopes and ridges. The dazzling diversity of forms and colors within this group reflects a similar diversity of physiological adaptations and life history strategies. Consider, for example, the ecological biographical, morphological and physiological spectra represented by just three of our 450 species of forbs – Scamman’s spring beauty (Claytonia scammaniana), tall bluebells (Mertensia paniculata), and round-leaved sundew (Drosera rotundifolia).

The families with the largest numbers of forbs in the park flora are:

• Aster family (Asteraceae, 59 species)
• Mustard family (Brassicaceae, 45 species)
• Buttercup family (Ranunculaceae, 32 species)
• Pink family (Caryophyllaceae, 31 species)
• Saxifrage family (Saxifragaceae, 31 species)

 

Ferns & Fern Allies

This is an evolutionarily ancient and very diverse group of plants that are often placed together in the taxonomic Division Pteridophyta, which is comprised of vascular plants that do not produce seeds, but instead reproduce through spores. Pteridophytes have two functional life stages, a free-living, independent gametophyte stage that produces motile sperm and a sporophyte stage (which is the stage we see, in the form of fronds and stipes). The morphological and evolutionary diversity contained within this division of the plant kingdom is considerable.

In Denali the “lower plants” in Division Pteridophyta are represented by the following groups: true ferns (Blechnaceae, Dryopteridaceae, Pteridaceae, Thelypteridaceae, and Polypodiaceae) the horsetails (Equisetaceae), Club mosses, (Lycopodiaceae), Spike mosses (Selaginellaceae) and quillworts (Isoetaceae).The most species-rich fern family in the Denali flora is the Wood fern family (Dryopteridaceae; 13 species), followed by the Maidenhair fern family (Pteridaceae; 3 species). There is one species each from the three other fern families that occur here: Deer fern family (Blechnaceae), Polypody family (Polypodiaceae), and Marsh fern family (Thelypteridaceae).

Closely related to the true ferns are an ancient and peculiar-looking group of spore-bearing plants appropriately called the Moonworts, which are placed by taxonomists in the Adder-tongue plant family (Ophioglossaceae). There are ten species of moonworts known to occur in the flora of Denali National Park and Preserve. Except for the most common member of this genus in the park, which is Botrychium lunaria, these species have very interrupted and spotty distribution patterns – they are found only rarely, even by the keenest observers. Moonworts are most commonly found in lush and moist (but not wet) meadow habitats in subalpine slopes and river terraces in association with dense growths of grasses such as Festuca altaica, Poa spp. and forbs, including wild geranium (Geranium erianthum), monkshood (Aconitum delphiniifolium) and veronica (Veronica wormskjoldii).

22 of the 28 fern and fern ally species occurring in the park are listed below.

Ferns:

• Cystopteris fragilis – brittle bladderfern
• Cystopteris montana – mountain bladderfern
• Dryopteris expansa – spreading woodfern
• Dryopteris fragrans – fragrant woodfern
• Gymnocarpium dryopteris – weatern oakfern
• Woodsia alpina – alpine woodsia
• Woodsia glabella – smooth woodsia
• Woodsia ilvensis – rusty woodsia

Fern Allies:

• Botrychium lunaria – common moonwort
• Botrychium minganense – Mingan moonwort
• Diphasiastrum alpinum – alpine clubmoss
• Diphasiastrum complanatum – groundcedar
• Equisetum arvense – field horsetail
• Equisetum fluviatile – water horsetail
• Equisetum palustre – marsh horsetail
• Equisetum pratense – meadow horsetail
• Equisetum scirpoides – dwarf scouringrush
• Equisetum sylvaticum – woodland horsetail
• Equisetum variegatum – variegated scouringrush
• Huperzia haleakalae – fir clubmoss
• Lycopodium annotinum – stiff clubmoss
• Lycopodium lagopus – one-cone clubmoss

 

Cottongrass (Eriophorum brachyantherum) is part of the sedge family.

NPS Photo / Jacob W. Frank

Grasses, Sedges, Rushes

Botanists call grasses and other grass-like plants “graminoids”. This diverse group of plants belongs to the taxonomic class called the monocots (Monocotyledoneae) – these are flowering plants (Angiosperms) that sprout a single seed-leaf when they germinate. The leaves of graminoids are generally long and linear in form and always exhibit a parallel pattern of venation. Monocots are one of the two primary classes of the flowering plants, along with the dicots (which sprout two seed leaves and have a “reticulate” or branching venation pattern).

After the forbs, graminoids are the most species-rich growth-form type represented in the vascular plant flora of Denali. There are 176 species from five different plant families of graminoids known to occur in Denali National Park and Preserve. The sedge family contributes by far the largest number of species of any vascular plant family to the flora of Denali, including 73 species of the genus Carex (the sedges), making it is the most species–rich genus in the park.

Graminoid plant families present in the park flora are as follows:

• Sedge family (Cyperaceae; 91 species)
• Grass family (Poaceae; 60 species)
• Rush family (Juncaceae; 21 species)
• Arrowgrass family (Juncaginaceae; 2 species)
• Cattail family (Typhaceae; 1 species)
• Pod grass family (Scheuchzeriaceae; 1 species)

Graminoid species are very well represented in Denali’s wetland flora. These plants often form the defining element of wetland plant communities – the familiar wet sedge meadow that lines the margins around ponds and in swampy openings within the boreal forest. Large, robust sedges such as Carex aquatilis, Carex utriculata, and Carex canescens are particularly plentiful in these wetland habitats. The graminoids are a very ecologically diverse group of plants, however, and are by no means restricted to marshy and wet sites in Denali. In fact, a diverse set of these plants, including many of the grasses and sedges (species from the families Poaceae and Cyperaceae) are found in the driest plant communities on the landscape – communities occupying steep south-facing slopes from the lowlands all the way to dry alpine ridges.

To most easily distinguish among the graminoids and determine when a plant is a grass, sedge, or rush, look to its stems. Sedge stems are generally triangular in cross-section and solid (not hollow), with the leaves in three rows. Rush stems are round and solid or pithy. Grass stems are round, jointed, often hollow, and with the leaves in two rows. Use a rhyme to help remember the distinctions between families of grass-like species: “Sedges have edges, rushes are round, and grasses have nodes where leaves are found.”

 

Stair-step Moss (Hylocomium splendens)

NPS Photo / Peter Nelson

Mosses & Liverworts

The mosses and liverworts, taken together along with hornworts, form the taxonomic division of the plant kingdom called the Bryophytes (Division Bryophyta), and are considered to be the first land plants. These small plants lack true stems, leaves, or roots but can appear structurally similar to other plants – with stem-like, leaf-like, and even root-like structures.

The body tissue of the gametophyte (the dominant part of the life cycle in bryophytes) lacks formal xylem and phloem conducting tissue like that exhibited by the vascular plant groups. Thus bryophytes cannot grow up far from the substrate that is their source of water and mineral nutrients. For example, a tree-sized moss would be anatomically impossible due to the fact that it could not translocate water very far against the force of gravity.

Despite these seeming disadvantages compared to the vascular plants, the bryophytes are superabundant in many subarctic vegetation types and plant communities. In fact, there are very good reasons to believe that mosses play the defining role in many areas of Denali’s landscape. The deep layer of moss that forms in the floor of our boreal forests and cotton-grass dominated bogs has profound influences on the physical and biological characteristics of these sites.

For example, the growth of permafrost under the insulative blanket provided by feather mosses (i.e., Hylocomium splendens or Pleurozium schreberi) in spruce forests results in radical changes in the soil temperature and moisture of a site, the amount of available nutrients, and the ability of vascular plants to become established, over time. Few species of vascular plants are actually capable of germinating and establishing viable populations through this deep blanket of feather mosses, thus many boreal vascular plant species require major fires or other disturbance of the moss layer in order to become established. Thus, the “climax” condition of many of the successional trajectories in boreal areas of the park might most usefully be defined by the humble moss layer as opposed to the more obvious tree canopy.

Although mosses are most abundant in mesic to wet environments within the park, they occur across the entire moisture gradient found in Denali’s landscapes. This is in part due to their ability to remain effectively dormant for long periods of time when conditions are not suitable for growth and reproduction. For example, mosses such as Rhytidium rugosum appear in boulder fields and very dry tundra on exposed- wind-blown ridges.

Approximately 500 species of bryophytes have been documented in Denali National Park and Preserve. Many mosses are difficult to distinguish to species in the field because the taxonomic characters that are required to identify them require observing individual cell shapes and sizes and cell arrangements within the thallus.

The species listed below are very common and relatively easy to recognize once you take a closer look.

• Aulocomnium palustre – glow moss
• Aulocomnium turgidum – hooded glow moss
• Hylocomium splendens – stair-step moss
• Pleurozium schreberi – big red stem
• Ptilium crista-castrensis – knight’s plume moss
• Polytrichum juniperinum – juniper hair-cap moss
• Polytrichum strictum – bog hair-cap moss
• Rhytidium rugosum – pipecleaner moss
• Sphagnum spp. – peat moss

 

Freckle Pelt Lichen (Peltigera aphthosa)

NPS Photo / Peter Nelson

Lichens

Lichens are not actually plants, but rather symbiotic organisms that are the result of a symbiotic relationship between an algae and/or cyanobacteria and a fungal “host”. The resulting organism is partnership technically known as a lichenized fungi. Interestingly, this entity generally takes on a form very different than either of the two free-living members of the partnership (the fungus and the algae and/or cyanobacteria), and also looks very different than a plant because it lacks any true roots, stems, or leaves. In general, the fungal “host” provides shelter and structure to translocate water and nutrients, and the algal and/or cyanobacterial partner provides nutrients to the organism – either through photosynthesis or nitrogen-fixation.

Lichens are very important components of subarctic and arctic ecosystems due to their role in weathering of rock and minerals and their contribution of nitrogen and other nutrients to the soil. Lichens are often the very first life forms to colonize freshly exposed rock surfaces high in the mountains, where they begin the very slow process of weathering minerals from the barren rock and incorporating them into their bodies. When the lichens subsequently decompose, these nutrients become available to other forms of plant life, literally breaking down rock into its component minerals that are then available for plant nutrition. Individual lichens can be more than a thousand years old. These organisms are remarkably resistant to changes in environmental conditions and they can remain dormant for long periods of time if conditions are not favorable to their growth.

The most frequently encountered lichens can be separated into four groups based on general body shape:

• Foliose lichens have leaf-like body parts that are generally flat in cross section with a defined top and bottom (2-dimensional).
• Fruticose lichens have a body form like that of a miniature shrub, with branches that are generally not flat in cross-section (are 3-dimensional).
• Squamose lichens  are scaly and made up of many small, rounded (but flat) lobes. They are a form intermediate between foliose and fruticose.
• Crustose lichens are very small, and grow crust-like very close to their substrate—usually rock, soil, or tree bark.

There are over 450 species of lichens that occur in Denali National Park and Preserve, but only a select few of the most frequently found are listed below:

• Cladonia rangiferina – reindeer lichen
• Cladonia stellaris – popcorn lichen
• Dactylina arctica – dead man’s fingers
• Flavocetraria cucullata – curled snow lichen
• Flavocetraria nivalis – flattened snow lichen
• Masonhalea richardsonii – tumbleweed lichen
• Peltigera aphthosa – freckle pelt
• Thamnolia vermicularis – white worm