The Basal Angiosperms are comprised of a separate lineages that branched off from other flowering plants at successive occasions before the appearance of the "true" dicots (Eudicots) in the fossil record. Although "Dicots" and Monocots were traditionally defined by a combination of characteristics (two seedling leaves vs. one, net vs. parallel leaf veination, circularly arranged vs. scattered vascular bundles, flower parts in multiples of 4 or 5 vs. multiples of 3, etc.), the basal angiosperms do not fit perfectly into either category, although these lineages were once grouped with dicots due to their leaf veination and possession of multiple seedling leaves (cotyledons). Basal Angiosperms often show combinations of the following traits: numerous flattened (laminar) stamens with wide filaments; numerous tepals; many separate carpels; aromatic oils (giving them a "primitive" odor); and alternate, spirally arranged leaves. Most also share the microscopic characteristic of monosulcate, or monoaperturate pollen (also seen in monocots). Phylotaxis was probably spiral in the flowers of the ancestor of all angiosperms. Basal Angiosperms are not a monophyletic group; it is really a term that applies to all the collective, unrelated angiosperm lineages other than Monocots and Eudicots.
There was some debate in the early 2000s as to whether Amborella, a dioecious shrub from New Caledonia, is the sole representative of the basalmost-branching lineage of angiosperms or whether the angiosperm order containing Water Lilies, Nymphaeales, is also on the branch most distantly related to all other angiosperms with Amborella. Although mitochondrial genes seem to support the latter hypothesis, both chloroplast and nuclear data have converged on Amborella by itself as the first-branching lineage of angiosperms. Nymphaeales and Amborella both seem to lack vessel elements homologous to those seen in practically all other angiosperms. They also both lack the ethereal oils (and thus the "primitive odor") that are present in most other basal angiosperm lineages. Although the basal angiosperm families collectively account for less than 5% of all angiosperm species, they contain much of the variation in floral structure, arrangement, and floral gene expression within flowering plants.
Basal angiosperm families covered in class:
- Amborellales: Amborellaceae (Amborella Family; you don't need to know how to ID the family, but you should know Amborella trichopoda)
- Nymphaeales: Nymphaeaceae (Water-Lily Family)
- Austrobaileyales: Order details; You aren't required to learn any families in this order, but you should know where it falls phylogenetically
- Magnoliales: Magnoliaceae (Magnolia Family)
- Piperales: Aristolochiaceae (Pipevine Family)
- Laurales: Lauraceae (Laurel Family)
- Order: Amborellales
Amborellaceae: (Amborella Family) 1 species
Characteristics: Contains only one species of shrub, Amborella trichopoda, from New Caledonia with alternate, toothed leaves. Dioecious, but probably a secondarily derived characteristic from a perfect-flowered ancestral angiosperm, as some Amborella shrubs can apparently change sex over the course of their lifetime, and female flowers with staminodes (sterile stamens) are frequent. Perianth is spirally arranged, with no clear distinction between sepals and petals. Male flowers have numerous spirally-arranged stamens, and female flowers have a few (less than 10) apocarpous ovaries that are incompletely sealed and develop into drupe-like fruits.
Interesting stuff: Not many people cared about this tiny-flowered New Caledonian shrub until the advent of DNA sequencing technology in the late 1990s. Once it was found to branch at or near the base of the angiosperm tree, it became the subject of many publications. It is now viewed as a keystone organism in understanding the characteristics of the ancestors of all flowering plants, as it may retain some ancestral morphology and genetics lost in the branch leading to all other angiosperms. It is important to note, however, that Amborella is a modern organism, not a fossil, and as such has had just as much time as any other flowering plant to evolve since the common ancestor of all modern angiosperms.
Nymphaeaceae: (Water-Lily Family) ∼70 species
Identification characteristics: The flowers of Water Lilies are variable in morphology, but are usually readily identifiable. They usually have few sepals (3-6) which merge into petaloid structures. The petals may be small and reduced or may be staminoid in structure. Often, the petals become more and more stamen-like until they eventually intergrade with the fertile, laminar stamens. The ovary is usually at least partially inferior and most often produces a leathery berry that ruptures irregularly, releasing seeds which are generally water-dispersed. Occasionally, separate carpels and superior ovaries may occur, particularly if the family Cabombaceae is included within Nymphaeaceae. The leaves are usually cordate to sagittate at the base, and petioles, peduncles, and flower buds are covered in slimy mucilage. With their showy flowers and aquatic habit, the only plant family likely to be confused with Nymphaeaceae is the unrelated Nelumbonaceae, which has peltate leaves and a superior ovary that forms a unique fruit-type (not at all like a leathery berry).
Interesting stuff: Despite their aquatic habitat, study of water-lily floral and vegetative structure helps provide insight into what features were present in the ancestor of all modern day angiosperms. Water-lilies were once hypothesized to be relatives of monocots and other herbaceous 'paleoherbs' because of similarities in pollen morphology and vascular arrangement. Water-lilies are important ornamental components of water gardens around the world. Cabombaceae is listed as a separate family in your flora.
(You should know the relative placement of Austrobaileyales in angiosperm phylogeny and some of the floral characteristics: spiral flower parts with no sepal/petal distinction, many spiral stamens, carpels spiral, apocarpous).
Magnoliaceae: (Magnolia Family) ∼250 species
Identification characteristics: Magnoliaceae have tepals in multiples of three which range in number from 6 to many. The outer 3 are often distinctly more sepaloid. The stamens are numerous and laminar. Carpels are numerous and arranged on an elongate receptacle in cone-like fashion. These separate carpels may sometimes form follicles that partially fuse before releasing arillate seeds, or may stay separate as an aggregation of wind-borne samaras. Leaves of Magnoliaceae are alternate and show a characteristic ring around the stem (a scar left by the deciduous stipules) at every petiole base and old node. Magnoliaceae also produce volatile oils that often make their vegetation aromatic when crushed.
Interesting stuff: Magnoliaceae have sometimes been hypothesized to be the basalmost angiosperm family due to the resemblance of their gynoecium to the cones of gymnosperms. However, this resemblance is superficial, and the structures are non-homologous. Magnolias and Tulip Tree are well-known ornamentals and valued timber trees.
Lauraceae: (Laurel Family) ∼2,978 species
Identification characteristics: Lauraceae are alternately-leaved shrubs or trees in our range. They can be identified by their 6 tepals, usually 9 stamens, anthers which release pollen through flapped valves, and a unilocular, superior ovary which forms a drupe as the fruit. Many species are dioecious (all in North Georgia), and many possess staminodes or glands in place of one or more whorls of stamens. All vegetative parts of Lauraceae are extremely fragrant when broken due to copius quantities of volatile turpenoids.
Interesting stuff: Lauraceae are one of the largest basal angiosperm families and are common in tropical forests. One genus, Cassytha, is parasitic and viney, strongly resembling members of the genus Cuscuta(Convolvulaceae: in Asterids) in a striking case of convergent evolution. Bay leaves, cinnamon, and avocado are important economically. Sassafras root was once the 2nd largest export from North America (behind tobacco) in colonial times, but tea and root beer produced from it has fallen into disfavor because of the presence of small quantities of carcinogenic compounds therein.
Aristolochiaceae: (Pipevine Family) ∼624 species
Identification characteristics: Flowers in Aristolochiaceae may be zygomorphic or actinomorphic. Most members lack petals, but have three pigmented sepals that are fused together. There are 6 to 12 stamens that are often semi-fused to the style, and the inferior ovary is comprised of 4 to 6 fused carpels. Most species produce capsules as the fruit. Aristolochiaceae have alternate leaves that are very often reniform or cordate in outline.
Interesting stuff: Many members of Aristolochiaceae produce maroon or brownish, foetid flowers that are carrion fly or beetle pollinated. The genus Aristolochia produces elaborate, curved calyx tubes that often trap flies until the flower withers. Members of the genus are often called "Pipevine" or "Dutchman's Pipe" for their shape. They produce Aristolochic Acids, which are concentrated in the wings of Pipevine Swallowtails to make them distasteful to predators. It is a strong-enough deterrant that it has shaped the evolution of many other eastern North American Butterfly species to be Batesian mimics of the black-and-blue color pattern of Pipevine Swallowtails.
Examples: Aristolochia arborea, (2), (3); A. fimbriata (side view); A. grandiflora (side view); A. macrophylla with Pipevine Swallowtail caterpillars, (flower closeup), (side view) Dutchman's Pipe; A. macroura, (2), (3); A. tomentosa, (closeup) Wooly Dutchman's Pipe; Asarum canadense, (closeup front), (closeup side) Wild Ginger; Hexastylis arifolia, (flowers, closer), (flowers, front); Little Brown Jug; Hexastylis speciosa Alabama Wild Ginger
- Piperaceae: Peperomia obtusiflora (closeup), Piper sp. (Costa Rica)
- Saururaceae: Saururus cernuus, (2), (3) Lizard's Tail