Ochnaceae
Ochnaceae is a family of flowering plants in the order Malpighiales. In the APG III system of classification of flowering plants, Ochnaceae is defined broadly, to include about 550 species, and encompasses what some taxonomists have treated as the separate families Medusagynaceae and Quiinaceae. In a phylogenetic study that was published in 2014, Ochnaceae was recognized in the broad sense, but two works published after APG III have accepted the small families Medusagynaceae and Quiinaceae. These have not been accepted by APG IV.
In this article, "Ochnaceae" will refer to the larger circumscription of the family, which is otherwise known as Ochnaceae sensu lato or as the ochnoids. In this sense the family includes 32 genera with about 550 species.
Ochnaceae, defined broadly or narrowly, is pantropical in distribution, with a few species cultivated outside of this range. Ochnaceae is most diverse in the Neotropics, with a second center of diversity in tropical Africa. It consists mostly of shrubs and small trees, and, in Sauvagesia, a few herbaceous species. Many are treelets, with a single, erect trunk, but low in height. The Ochnaceae are notable for their unusual leaves. These are usually shiny, with closely spaced, parallel veins, toothed margins, and conspicuous stipules. Most of the species are buzz pollinated. In eight of the genera in tribe Sauvagesieae, the flower changes form after opening, by continued growth of tissue within the flower.
A few species of Ochna are cultivated as ornamentals. Ochna thomasiana is probably the most commonly planted, but it is often misidentified in the horticultural literature.
The leaves of Cespedesia are sometimes to in length and are used for roofing. An herbal tea is made from the pantropical weed Sauvagesia erecta.
In its evolution, Ochnaceae has been unusual, in "reverting" to character states that are regarded as ancestral or primitive. For example, an actinomorphic floral symmetry has appeared twice in the subfamily Ochnoideae. Also, two clades of Ochnaceae, one in Ochnoideae and another in Quiinoideae have a derived condition very close to apocarpy. The complete separation of the carpels is thought to be the ancestral state for angiosperms.
Fossils attributed to Ochnaceae are known from the early Eocene of Mississippi. The age of the family is very roughly estimated at 100 million years.
A great many genus names have been published in Ochnaceae. In a taxonomic revision of Ochnaceae, as three families, in 2014, only 32 of these genera were accepted; one in Medusagynaceae, four in Quiinaceae, and 27 in Ochnaceae s.s. In that same year, a 33rd genus, Neckia, was reestablished in order to preserve the monophyly of another genus, Sauvagesia.
The largest genera in Ochnaceae are: Ouratea, Ochna, Campylospermum, Sauvagesia, and Quiina. None of the larger genera has been the subject of a phylogenetic analysis of DNA sequences of selected genes. In one study of the subfamily Quiinoideae, based on the trn L-F intergenic spacer, only nine species were sampled from this subfamily.
Genera
The following list of 36 genera consists of Neckia, which was resurrected in 2014, Indovethia, Polythecanthum and Sinia, plus the 32 genera that were described in the most recent revision of Ochnaceae. The classification is from Schneider et alii.Description
The following description is excerpted from the descriptions of Medusagynaceae, Quiinaceae, and Ochnaceae s.s. in The Families and Genera of Vascular Plants, with some information from other sources, as indicated.Mostly shrubs and small trees, plus a few trees of moderate size, and in Sauvagesia, a few herbs.
Leaves simple, except pinnately compound in Krukoviella, and in Quiinoideae, often pinnately lobed or compound on juvenile plants. Pinnate leaves are typical of Rhytidanthera. The leaves are often coriaceous and conspicuously serrate. Stipules present, except Medusagyne.
Venation often scalariform in appearance, with parallel and closely spaced secondary and tertiary veins. Petioles absent or short, sometimes resembling a pulvinus.
Unisexual flowers are common in Medusagyne and in Quiinoideae, but restricted to a clade of three genera in Ochnoideae. Unisexual flowers are found in Schuurmansia, Schuurmansiella, and Euthemis. The flowers are always unisexual in Schuurmansiella.
In polygamous species, flowers have been assessed as bisexual on the basis of morphology only. Pollen produced by apparently hermaphroditic flowers has, in a few cases, been found to be inaperturate, rendering the flower functionally female.
Sepals 3 to 5, often unequal, sometimes accrescent.
Petals 4 or 5, or rarely 3, 6, 7, or 8, often contort, free or fuzed at base only, sometimes reflexed over the sepals.
Fertile stamens 5 to 10 or numerous, rarely one. Filaments sometimes persistent, sometimes narrowed near the anthers.
Anthers basifixed or slightly dorsifixed, usually dehiscing by one or two apical or subapical pores, sometimes latrorsely by longitudinal slits. In Medusagyne and Quiinoideae, an enlarged septum separates the thecae.
Staminodes often present, free or connate, sometimes petaloid, sometimes enveloping the fertile stamens.
Nectar not produced. Flowers usually buzz-pollinated.
Ovary superior, longitudinally ribbed in Medusagyne and Quiinoideae; unribbed in Ochnoideae. Carpels completely fused or nearly separate; 2-15, or up to 25 in Medusagyne. Style apical or gynobasic.
Fruit sometimes winged; rarely a nut or drupe, often berry-like; usually a septicidal capsule, or else the ovary separating to form blackish drupelets on a usually reddish, accrescent receptacle.
Seeds albuminous or exalbuminous, winged or not. The seed coat often includes a layer of cristarque cells. These are sclereids, each containing calcium oxalate crystals in the form of a druse.
Classification
Until near the end of the 20th century, Ochnaceae was regarded as a rather odd family, difficult to place with a high degree of certainty. Even into the 21st century, some authors treated the genus Strasburgeria as the closest relative of Ochnaceae, and some even placed it within the family. In the APG III system, Strasburgeria is grouped with Ixerba to form the family Strasburgeriaceae in the rosid order Crossosomatales.More rarely, the genus Diegodendron was thought to be close to Strasburgeria and Ochnaceae. Molecular phylogenetic studies have strongly supported the inclusion of Diegodendron in the rosid order Malvales, and it is sometimes treated as a monospecific family therein. Otherwise, it has been placed in Bixaceae, though there is reason to suspect that it might be closer to Sphaerosepalaceae.
All of the genera mentioned above, as well as Ochnaceae, were long regarded as anamalous taxa of uncertain affinity. All had been placed, at one time or another, with Ochnaceae, near Theaceae, a family now included in the basal asterid order Ericales.
In 2012, an analysis of chloroplast DNA resolved Ochnaceae as sister to a group of five families known as the clusioids. This result had only weak bootstrap support. The clusioids were once regarded as a group of four families, but Clusiaceae was divided in 2009 and the name Calophyllaceae was resurrected for one of the resulting segregates.
There are only a few morphological characters that unite the clusioids with Ochnaceae. The petal aestivation is often contort in the clusioids, and usually so in Ochnaceae. In both groups, the flowers usually bear numerous stamens, and in the ovary, the placentation is mostly axile. In the ovules, the nucellus is often thin, and the outer integument is usually thicker than the inner.
Taxonomy
Ochnaceae is divided into three subfamilies: Medusagynoideae, Quiinoideae, and Ochnoideae.A molecular phylogenetic study resolved Medusagynoideae and Quiinoideae as sister subfamilies, but this result had only weak statistical support. In both subfamilies, the flowers are polystemonous. Except for the genus Froesia, many or all of the flowers are unisexual. The anthers contain a massive septum between the thecae that persists after anther dehiscence. The styles radiate outward from the ovary. At anthesis, the ovary is sculpted with longitudinal ribs.
Medusagynoideae consists of a single species, Medusagyne oppositifolia. It is endemic to the island of Mahé in the Seychelles.
Quiinoideae comprises about 48 species in four genera: Froesia, Quiina, Touroulia, and Lacunaria. It is restricted to tropical America. Froesia is distinct from the other three genera. Its flowers are always bisexual, and the fruit consists of three structures that resemble follicles, except that they are not quite entirely separate from each other.
The subfamily Ochnoideae was revised in 2014 as Ochnaceae sensu stricto. In that treatment, 27 genera were described. An additional genus, Neckia, was resurrected in that same year, based on the results of a molecular phylogenetic study. Amaral and Bittrich divided Ochnoideae into three tribes: Luxemburgieae, Sauvagesieae, and Ochneae. The genus Testulea was included in the tribe Sauvagesieae. No subtribes were recognized.
In 2014, a second reclassification of Ochnoideae was published, based on cladistic analysis of DNA sequences. In that paper, Schneider et alii divided Ochnoideae into four tribes: Testuleeae, Luxemburgieae, Sauvagesieae, and Ochneae. Their circumscription of the tribes was the same as that of Amaral and Bittrich, except that Testulea was removed from Sauvagesieae into its own tribe, Testuleeae. Inclusion of Testulea in Sauvagesieae renders that tribe paraphyletic over Luxemburgieae.
Testulea consists of a single species, Testulea gabonensis, that is endemic to Gabon. It is unique in Ochnoideae in that its leaves have a brochidodromous pattern of venation and its flowers are tetramerous. In addition, only one of the stamens is fertile. The others are modified into staminodes and united into a column for up to 2⁄3 of their length.
The tribe Luxemburgieae consists of two genera: Philacra and Luxemburgia. Philacra is native to Venezuela and northern Brazil. Luxemburgia is from Brazil.
The tribe Sauvagesieae is pantropical in distribution, and consists of 16 genera, most of them small. The largest, by far, is Sauvagesia, with 38 species, 35 of which are restricted to the neotropics. Sauvagesia is heterogeneous, and might be paraphyletic, even with Neckia removed from it. Relationships in the tribe Sauvagesieae are not well understood, and for this reason, it has not been divided into subtribes.
The tribe Ochneae is found in most of the tropics, but is most abundant in Africa and tropical America. It is distinguished from the rest of Ochnoideae by the absorption of the endosperm before the seed reaches maturity. Its nine genera belong to three subtribes: Lophirinae, Elvasiinae, and Ochninae.
The subtribe Lophirinae consists of a single genus, Lophira. It has two species, both confined to tropical Africa. It produces an unusual fruit, in which two of the sepals become greatly enlarged and form wings that facilitate seed distribution by wind.
The subtribe Elvasiinae consists of two genera, Perissocarpa and Elvasia, both confined to the American tropics. Perissocarpa has never been sampled for a molecular phylogenetic study.
The subtribe Ochninae consists of six genera: Campylospermum, Ouratea, Idertia, Brackenridgea, Rhabdophyllum, and Ochna. The largest of these, Ouratea, is confined to the New World and contains all of the New World species in Ochninae. All of the genera in Ochneae appear to be monophyletic, as defined by Amaral and Bittrich, but in one molecular phylogenetic study, Ouratea and Ochna received only weak bootstrap support in the maximum likelihood analysis. Idertia and Brackenridgea are probably sister genera, but no other relationships have been resolved among the genera of Ochninae.