Franklin, R.S.
PL S 572 Term Paper
The Rhoadales: A disbanded order
REBECCA S. FRANKLIN
Laboratory of Tree-Ring Research, Department of Geosciences, University of Arizona, Tucson,
AZ, 85721
rebecca@ltrr.arizona.edu
ABSTRACT
--------------Rhoeadales, an order described by Engler and Diels (1936) and circumscribing eight
families, the Papaveraceae, Fumariaceae, Capparaceae, Brassicaceae, Tovariaceae, Resedaceae,
Moringaceae and the Bretschneideraceae has been since disbanded by subsequent taxonomic
circumscriptions. Cronquist’s circumscription in 1988 grouped the families into three orders, the
Papaverales, the Capparales and the Sapindales and the Angiosperm Phylogeny Group II (APG
II) in 2003 further reduced the orders containing these families into two orders, the Ranunculales
and the Brassicales (Figure 1). In this paper I will describe the basic characteristics of the
abovementioned eight families and discuss the reasons for Engler’s grouping of these families
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PL S 572 Term Paper
into one order, the Rhoeadales, and then the reasons for the reorganization of these families in
the circumscriptions of Cronquist and APG II.
The first comprehensive system of plant taxonomy was Adolf Engler’s. In his book, Die
Natürlichen Pflanzenfamilien (1915) he based his taxonomy of the orders and families of plants
on the complexity of floral morphology. His assumptions of evolutionary trends were from
simple to complex (gaining parts), free to joined, superior to inferior ovaries and actinomorphic
to zygomorphic corollas. The Rhoeadales, as Engler grouped them are unified by characteristics
such as leaf morphology, petal and stamen number, inflorescence type. The characteristics of the
families circumscribed in Rhoeadales are as follows. I will describe characteristics that unify
these families morphologically according to Engler’s circumscription into one order and also lay
the groundwork for the some of the differences they have that will land them in separate orders
later on.
Papaveraceae
Papaveraceae are herbaceous annuals or perennials that have highly dissected simple
leaves that are alternalte or basal. They have showy actinomorphic flowers that are solitary to
cymose and crumpled while in the bud. Two deciduous sepals are present while petals are
usually four to six. The compound pistil has two to several carpels and the stigma and style are
solitary. Papaveraceae have numerous hypogynous stamens, munerous ovules with parietal
placentation and a superior ovary. Papaveraceae are broadly distributed throughout the northern
hemisphere in subtropical environs and through the west coast of South America
Fumariaceae
Fumariaceae differ from the Papaveraceae in that they have only two carpels, four to six
stamens (2-adelphous with two bundles of three stamens), and zygomorphic flowers with
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PL S 572 Term Paper
distinctive two-merous dissymmetric flowers, usually spurred with a small to invisible calyx.
Fumariaceae are similar to the Papaveraceae in their foliage, single to solitary inflorescences,
having two sepals and the common occurrence of latex in the vegetative tissue.
Capparaceae
This family contains usually woody climbing plants with simple to palmately compound
alternate leaves, actinomorphic to zygomorphic, perfect racemose polypetalous flowers. These
plants have two to six sepals and petals. The androecium is hypogynous with six to numerous
showy stamens with long filaments. The single pistil has two carpels and a distinctive superior
ovary on a long gynophore. The ovary has parietal placentation, the ovules form indehiscent
siliques or silicles lacking a replum, or a false septum. Capparaceae also contain mustard oils.
Although having a wide distribution, these primitive plants are adapted to dry conditions in the
tropics and subtropics mainly.
Brassicaceae
Brassicaceae differ from the Capparaceae in that they herbaceous with stellate or
dendritic hairs, they have simple often highly divided leaves and their flowers are always in
racemes. Additionally, the flower is always four-merous with tetradynamous stamen and the fruit
always has a replum or false septum. The similarities are that Brassicaceae has mustard oils, one
pistil, two carpels, a superior ovary, parietal placentation and ovules that form siliques or silicles.
Distribution of Brassicaceae is world wide.
The following four smaller families have a more limited tropical to subtropical
distribution.
Tovariaceae
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PL S 572 Term Paper
These plants are herby to shrubby and like the above families have racemose
inflorescences. They have trifoliate stipulate leaves have six- to nine-merous shortly clawed to
sessile polypetalous flowers with a short style and spreading stigma. The anthers as well are sixto nine-merous and the fruit is a berry. Tovariaceae also have mustard oils.
Resedaceae
Resedaceae have leaves with entire to pinnatifid leaves that are alternate to spiral. These
Mediterranean herbs and shrubs are usually xerophytic.
The inflorescence is terminal and
racemose with small zygomorphic six-merous bracteate flowers. The petals are fringed with the
adaxial petal being the larest. The flowers have an obvious hypanthium three to six carpels, one
ovary and locule with a capsular or berry fruit. Mustard oils are also present in this family.
Moringaceae
These are woody stout stemmed trees and shrubs that also contain mustard oils. Their
deciduous leaves are pinnarely compound with conspicuous strongly scented glands at the base.
The five-merous flowers are arranged in panicles with the floral receptacle developing a
gynophore. The androecium is two whorled.
Bretschneideraceae
Bretschneideraceae are trees with decidous alternate pinnately compound leaves. As with
many families in the Rhoeadales, they have flowers aggregated in terminal racemes. These large
flowers are zygomorphic, polypetalous, with a five-merous calyx and corolla. Carpels are three
to five with two to three ovules per locule. This family has eight stamens with hairy filaments.
Once more mustard oils are found in this family in the Rhoeadales.
The order Rhoeadales on the whole, is temperate in distribution, containing some rather
primitive plants such as the Resedaceae and the Papaveraceae and some more specialized
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PL S 572 Term Paper
species, such as those found in the Brassicaceae (Bews 1927). The morphological similarities
that Engler used in delineating this order are the inflorescence structure (usually cymose or
panniculate), the highly dissected simple leaves (or in some cases compound) and the numerous
stamens (in most cases). Another example of what Engler used to delineate this order is the
examination of the torus, or the floral receptacle and the nectary characteristics. Norris, in 1941,
commented on Engler’s Rhoeadales mentioning that the floral nectarines in Rhoeadales appear to
have originated independently of the other parts. He also noted that details of the vascular
bundle distribution in the Rhoeadales’ torus and also the distribution of the nectarines appear to
be useful in comparing taxa in this family with respect to their phylogenetic relationships. By
examining this characteristic of the flower, Norris states that it appears that the Capparaceae and
the Resedaceae are the most primitive families of the Rhoeadales based on the fact that they
seem to come from an ancestral group that did not have connections between the nectarines and
sepal and petal vascular bundles. Using this line of reasoning, he also concludes that the
Papaveraceae, Fumariaceae and Brassicaceae (then called Cruciferae) were derived from
ancestral groups resembling the existing Resedaceae and Capparaceae. The argument supporting
Papaveraceae being relatively “new” is that it has an absence of any nectarines on its torus and
therefore cannot have given rise to any of the other families in the Rhoeadales. This reasoning
follows Engler’s use of parsimony in determining phylogenetic relationships.
Cronquist’s circumscription
In his 1988 book the evolution and Classification of Flowering Plants, Cronquist states
that the method he follows is the Besseyan method which starts out with groups that have
evolved the least from their ancestral prototype rather than the taxa that are the most advanced in
their descent. Cronquist uses a phylogenetic approach yet classifies taxa in a way that best
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circumscribes their similarities and differences. Cronquist does not use molecular data as he sees
it as different from and more limiting than morphological data. Still, he uses chemical and
microscopic data in his circumscriptions (Cronquist 1988).
Cronquist groups the families of the former Rhoeadales into three orders, the Papaverales
(containing Papaveraceae and Fumariaceae), the Capparales (containing Capparaceae,
Brassicaceae, Tovariaceae, Resedaceae and Moringaceae) and the Sapindales (containing
Brethschneideraceae).
To group together the first order, the Papaverales, Cronquist uses the morphological
features of 2 sepals and three-aperature pollen and also the chemical characteristics of the
absence of ethereal oils and the presence of isoquinoline alkaloids.
Another factor that
conscribes this group is that it is of relatively recent origin compared to the rest of the former
Rhoeadales families.
The second family, the Capparales have a similar combination of morphological and
chemical characteristics to join the families together. Families in the Capparales have compound
leaves, parietal placentation and hypogynous stamens but they also have a more rigorous
characteristic- the presence of glucosinolates (mustard oils).
The Sapindales have a set of characteristics that only all occur together in this order. The
combination of compound or cleft leaves, haplostemenous/diplostemenous androeciums well
developed nectary disks, syncarpous ovaries and one to two ovules per ovary all indicate a
member of the Sapindales. In these three orders we can see a progression from the wholly
morphological characteristics used by Engler to circumscribe families to an inclusion of factors
that increasing levels of technology allow for, such as pollen characteristics and alkaloid
identification.
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APG II 2003 Circumscription
LITERATURE CITED
ANGIOSPERM PHYLOGENY GROUP. 2003. An update of the Angiosperm Phylogeny
Group classification for the orders and families of flowering plants: APG II. Botanical
Journal of the Linnean Society 141: 399-436.
BEWS, J.W. 1927. Studies in the Ecological Evolution of the Angiosperms. New Phytologist 26
(2): 65 – 84.
CRONQUIST, A. 1988. The evolution and classification of flowering plants. 2 Ed. Bronx: nd
The New York Botanical Garden.
ENGLER, A, and L. DIELS. 1936. Syllabus der pflanzenfamilien. Aufl. 11. Berlin: Gebrüder
Borntraeger.
JUDD, W. S., C. S. CAMPBELL, E. A. KELLOGG, P. F. STEVENS and M. J. DONOGHUE.
2003. Plant systematics: a phylogenetic approach. 2 Ed. Sunderland, MA: Sinauer nd
Associates, Inc.
NORRIS, T. 1941. Torus anatomy and nectary characteristics as phylogenetic criteria in the
Rhoeadales. American Journal of Botany28:101 – 113.
RONSE DE CRAENE L.P., T. Y. A. YANG, P. SCHOLS and
E. F. SMETS. 2002. Floral anatomy and systematics of Bretschneidera (Bretschneideraceae)
Botanical Journal of the Linnean Society, 139: 29–45.
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Figure 1. Changing distribution of “Rhoeadales"
Family
Engler (1936)
Cronquist (1988)
APG II (2003)
Papaveraceae
Rhoeadales
Papaverales
Ranunculales
Fumariaceae
Rhoeadales
Papaverales
Ranunculales
Capparidaceae (aka
Cappadaceae)
Rhoeadales
Capparales
Brassicales (in
“Brassicaceae”)
Brassicaceae
Rhoeadales
Capparales
Brassicales
Tovariaceae
Rhoeadales
Capparales
Brassicales
Resedaceae
Rhoeadales
Capparales
Brassicales
Moringaceae
Rhoeadales
Capparales
Brassicales
Bretschneideraceae
Rhoeadales
Sapindales
Brassicales
Figure 2. Complete families accompanying Rhoeadales distribution
A Engler (1936)
B. Cronquist (1988)
C. APG II (2003)
Rhoeadales
Papaverales
Ranunculales
Papaveraceae
Fumariaceae
Papaveraceae (incl.
Chelidoniaceae,
Eschscholziaceae,
Platystemonaceae)
Fumariaceae (incl. Hypecoaceae,
Pteridophyllaceae)
Papaveraceae (incl.
Eschscholziaceae, Hypecoaceae,
Platystemonaceae)
Fumariaceae
Kingdoniaceae
Eupteleaceae
Lardizabalaceae (incl.
Decaisneaceae
Sargentodoxaceae,
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PL S 572 Term Paper
Sinofranchetiaceae),
Menispermaceae
Berberidaceae (incl.
Epimediaceae, Leonticaceae,
Nandinaceae Podophyllaceae,
Ranzaniaceae)
Circaeasteraceae
Pteridophyllaceae
Ranunculaceae (incl.
Glaucidiaceae, Helleboraceae,
Hydrastidaceae,
Thalictraceae)
A. Engler (1936)
cont’d
Rhoeadales
B. Cronqist (1998) Cont’d
C. APG II (2003) cont’d
Capparales
Brassicales
Capparadaceae
Tovariaceae
Akaniaceae
Brassicaceae
Capparaceae (incl. Cleomaceae,
Koeberliniaceae,
Pentadiplandraceae)
Bretschneideraceae (in
Akaniaceae)
Tovariaceae
Brassicaceae
Bataceae
Resedaceae
Moringaceae
Moringaceae
Bretschneideraceae
Resedaceae
Brassicaceae (incl. Capparaceae,
Cleomaceae, Oxystilidaceae)
Caricaceae
Emblingiaceae
Sapindales
Staphyleaceae (incl.
Tapisciaceae)
Melianthaceae
Gyrostemonaceae
Bretschneideraceae
Limnanthaceae
Akaniaceae
Moringaceae
Sapindaceae (incl.
Ptaeroxylaceae)
Hippocastanaceae
Pentadiplandraceae
Aceraceae
Salvadoraceae
Burseraceae
Setchellanthaceae
Anacardiaceae (incl.
Blepharocaryaceae, Pistiaceae,
Podoaceae)
Julianaceae
Tovariaceae
Koeberliniaceae
Resedaceae
Tropaeolaceae
Simaroubaceae (incl.
Irvingiaceae, Kirkiaceae)
Cneoraceae
Meliaceae (incl. Aitoniaceae)
Rutaceae (incl. Flindersiaceae)
Zygophyllaceae (incl.
Balanitaceae,
Nitrariaceae, Peganaceae,
Tetradiclidaceae, Tribulaceae)
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Figure 3. APG II classification of Ranunculales
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Figure 4. APG II classification of Brassicales
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Figure 5. Cronquist classification v. APG II classification
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