Rafflesiaceae | |
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Rafflesia keithii flower | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Clade: | Eudicots |
Clade: | Rosids |
Order: | Malpighiales |
Family: | Rafflesiaceae Dumort. |
Genera [1] | |
Rafflesia R.Br. ex Gray Contents |
The Rafflesiaceae are a family of rare parasitic plants comprising 36 species in 3 genera found in the tropical forests of east and southeast Asia, including Rafflesia arnoldii , which has the largest flowers of all plants. The plants are endoparasites of vines in the genus Tetrastigma (Vitaceae) and lack stems, leaves, roots, and any photosynthetic tissue. They rely entirely on their host plants for both water and nutrients, and only then emerge as flowers from the roots or lower stems of the host plants.
Rafflesiaceae flowers mimic rotting carcasses in scent, color, and texture to attract their pollinators, carrion flies. For this reason, some flowers of the family Rafflesia are nicknamed "corpse flowers". Most members of Rafflesiaceae possess a large, bowl-shaped floral chamber formed by a perianth tube and a diaphragm. This diaphragm is the opening for carrion fly pollinators and is surrounded by attractive sterile organs. Flowers are generally unisexual, and can range from tens of cm to over a meter large. [2] [3]
Past taxonomic works have varied as to the classification of Rafflesiaceae. The classification of Rafflesiaceae has been somewhat problematic due to their highly reduced vegetative parts, modified reproductive structures, and anomalous molecular evolution (Davis 2008). Rafflesiaceae lacks rbcL and other plastid genes commonly used for phylogenetic inference in green plants. In fact, Molina et al. (2014) found that a genus of Rafflesia is the first parasitic plant studied containing no recognizable remnants of the chloroplast genome.
Most traditional classifications that were based entirely on morphological features considered Rafflesiaceae sensu lato (in the broad sense) to include nine genera, but the heterogeneity among these genera caused early workers, such as Harms (1935), to recognize four distinct groups that were then classified as tribes (still within Rafflesiaceae). This tribal system was followed by Takhtajan et al. (1985).
The first molecular phylogenetic study (using DNA sequences) that showed two of these tribes were not related was by Barkman et al. (2004). This study showed three genera (corresponding to tribe Rafflesieae, that is, Rafflesia, Rhizanthes, and Sapria) were components of the eudicot order Malpighiales. The genus Mitrastemon (tribe Mitrastemoneae) was shown to be unrelated and a member of the order Ericales. Later that year, Nickrent et al. (2004), using additional molecular data, confirmed the placements by Barkman et al. (2004) and also examined the positions of the two other tribes, Cytineae (Bdallophyton and Cytinus) and Apodantheae (Apodanthes, Berlinianche, and Pilostyles). Nickrent et al. (2004) showed Cytineae was related to Malvales and Apodantheae to either Malvales or Cucurbitales. Apodantheae has since been confirmed to be in the Cucurbitales (Filipowicz and Renner 2010).
Thus, the group traditionally classified as a single family, Rafflesiaceae, was actually composed of at least four distinct and very distantly related clades, with their similarities due to convergent evolution under their common parasitic lifestyle. A goal of taxonomy is to classify together only plants that all share a common ancestor, i.e., are monophyletic. Thus, the original Rafflesiaceae sensu lato is currently split into four families: [4]
These four families can be easily distinguished by floral and inflorescence features:
Early work on higher-level relationships was able to place Rafflesiaceae (in the strict sense) within the order Malpighiales, but was not able to resolve the closest ancestor within the order. [5] A 2007 phylogenetic analysis found strong support for Rafflesiaceae being derived from within Euphorbiaceae as traditionally circumscribed, which was surprising as members of that family typically have very small flowers. According to this analysis, the rate of flower size evolution was more or less constant throughout the family, except at the origin of Rafflesiaceae – a period of about 46 million years between when the group split from the Euphorbiaceae sensu stricto, and when the existing Rafflesiaceae split from each other – where the flowers rapidly evolved to become much larger before reverting to the slower rate of change. [6]
To maintain monophyletic families, in 2016 the APG IV system separated the family Peraceae from the Euphorbiaceae. [7] A summary cladogram is shown below, [6] with family placements in the APG IV system. [7]
Euphorbiaceae sensu lato |
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A more recent study has been provided by Liming Cai et al. (2021) [8]
A number of mitochondrial genes in the Rafflesiaceae appear to have come from their hosts (Tetrastigma). Because the hosts are not closely related to the parasites (as shown by molecular phylogeny results for other parts of the genome), this is believed to be the result of horizontal gene transfer. [9] [10] Especially high rates of HGT have been found to take place in Rafflesiaceae mitochondrial genes when compared to nuclear genes and to HGT in autotrophic plants. [11]
The Cucurbitales are an order of flowering plants, included in the rosid group of dicotyledons. This order mostly belongs to tropical areas, with limited presence in subtropical and temperate regions. The order includes shrubs and trees, together with many herbs and climbers. One major characteristic of the Cucurbitales is the presence of unisexual flowers, mostly pentacyclic, with thick pointed petals. The pollination is usually performed by insects, but wind pollination is also present.
The Malpighiales comprise one of the largest orders of flowering plants, containing about 36 families and more than 16,000 species, about 7.8% of the eudicots. The order is very diverse, containing plants as different as the willow, violet, poinsettia, manchineel, rafflesia and coca plant, and are hard to recognize except with molecular phylogenetic evidence. It is not part of any of the classification systems based only on plant morphology. Molecular clock calculations estimate the origin of stem group Malpighiales at around 100 million years ago (Mya) and the origin of crown group Malpighiales at about 90 Mya.
Rosales is an order of flowering plants. It is sister to a clade consisting of Fagales and Cucurbitales. It contains about 7,700 species, distributed into about 260 genera. Rosales comprise nine families, the type family being the rose family, Rosaceae. The largest of these families are Rosaceae (90/2500) and Urticaceae (54/2600). The order Rosales is divided into three clades that have never been assigned a taxonomic rank. The basal clade consists of the family Rosaceae; another clade consists of four families, including Rhamnaceae; and the third clade consists of the four urticalean families.
The Saxifragales (saxifrages) are an order of flowering plants (Angiosperms). They are an extremely diverse group of plants which include trees, shrubs, perennial herbs, succulent and aquatic plants. The degree of diversity in terms of vegetative and floral features makes it difficult to define common features that unify the order.
Rafflesia is a genus of parasitic flowering plants in the family Rafflesiaceae. The species have enormous flowers, the buds rising from the ground or directly from the lower stems of their host plants; one species has the largest flower in the world. Plants of the World Online lists up to 41 species from this genus, all of them are found throughout Southeast Asia.
Under the International Code of Nomenclature for algae, fungi, and plants (ICN), Rosidae is a botanical name at the rank of subclass. Circumscription of the subclass will vary with the taxonomic system being used; the only requirement being that it includes the family Rosaceae.
The Celastrales are an order of flowering plants found throughout the tropics and subtropics, with only a few species extending far into the temperate regions. The 1200 to 1350 species are in about 100 genera. All but seven of these genera are in the large family Celastraceae. Until recently, the composition of the order and its division into families varied greatly from one author to another.
The Flacourtiaceae is a defunct family of flowering plants whose former members have been scattered to various families, mostly to the Achariaceae and Salicaceae. It was so vaguely defined that hardly anything seemed out of place there and it became a dumping ground for odd and anomalous genera, gradually making the family even more heterogeneous. In 1975, Hermann Sleumer noted that "Flacourtiaceae as a family is a fiction; only the tribes are homogeneous."
Orobanchaceae, the broomrapes, is a family of mostly parasitic plants of the order Lamiales, with about 90 genera and more than 2000 species. Many of these genera were formerly included in the family Scrophulariaceae sensu lato. With its new circumscription, Orobanchaceae forms a distinct, monophyletic family. From a phylogenetic perspective, it is defined as the largest crown clade containing Orobanche major and relatives, but neither Paulownia tomentosa nor Phryma leptostachya nor Mazus japonicus.
Phyllanthaceae is a family of flowering plants in the eudicot order Malpighiales. It is most closely related to the family Picrodendraceae.
Peridiscaceae is a family of flowering plants in the order Saxifragales. Four genera comprise this family: Medusandra, Soyauxia, Peridiscus, and Whittonia., with a total of 12 known species. It has a disjunct distribution, with Peridiscus occurring in Venezuela and northern Brazil, Whittonia in Guyana, Medusandra in Cameroon, and Soyauxia in tropical West Africa. Whittonia is possibly extinct, being known from only one specimen collected below Kaieteur Falls in Guyana. In 2006, archeologists attempted to rediscover it, however, it proved unsuccessful.
Hydnoroideae is a subfamily of parasitic flowering plants in the order Piperales. Traditionally, and as recently as the APG III system it given family rank under the name Hydnoraceae. It is now submerged in the Aristolochiaceae. It contains two genera, Hydnora and Prosopanche:
Dipentodon is a genus of flowering plants in the family Dipentodontaceae. Its only species, Dipentodon sinicus, is a small, deciduous tree native to southern China, northern Myanmar, and northern India. It has been little studied and until recently its affinities remained obscure.
Cytinaceae is a family of parasitic flowering plants. It comprises two genera, Cytinus and Bdallophytum, totalling ten species.
The basal angiosperms are the flowering plants which diverged from the lineage leading to most flowering plants. In particular, the most basal angiosperms were called the ANITA grade, which is made up of Amborella, Nymphaeales and Austrobaileyales.
When the APG II system of plant classification was published in April 2003, fifteen genera and three families were placed incertae sedis in the angiosperms, and were listed in a section of the appendix entitled "Taxa of uncertain position".
The family Apodanthaceae comprises about 10 species of endoparasitic herbs. They live in the branches or stems of their hosts, emerging only to flower and fruit. The plants produce no green parts and do not carry out any photosynthesis. There are two genera: Pilostyles and Apodanthes. A third genus, Berlinianche, was never validly published. Mitochondrial and nuclear DNA sequences confidently place the Apodanthaceae in the Cucurbitales, where they also fit well in terms of their flower morphology.
Pilostyles is a genus of flowering plants in the family Apodanthaceae. It includes about 11 species of very small, completely parasitic plants that live inside the stems of woody legumes. Plants of this genus are sometimes referred to as stemsuckers.
In phylogenetic nomenclature, the Pentapetalae are a large group of eudicots that were informally referred to as the "core eudicots" in some papers on angiosperm phylogenetics. They comprise an extremely large and diverse group that accounting about 65% of the species richness of the angiosperms, with wide variability in habit, morphology, chemistry, geographic distribution, and other attributes. Classical systematics, based solely on morphological information, was not able to recognize this group. In fact, the circumscription of the Pentapetalae as a clade is based on strong evidence obtained from DNA molecular analysis data.
Daniel Lee Nickrent is an American botanist, working in plant evolutionary biology, including the subdisciplines of genomics, phylogenetics, systematics, population genetics, and taxonomy. A major focus has been parasitic flowering plants, particularly of the sandalwood order (Santalales). His interest in photographic documentation and photographic databases has led to several photographic databases including Parasitic Plant Connection, Phytoimages, Plant Checklist for the Rocky Mountain National Park, and Plant Checklist for the Crab Orchard National Wildlife Refuge.