represents its genus and its species within the genus, resulting in a single worldwide name for each organism. for example, the tiger lily is lilium columbianum. lilium is the genus, and columbianum the specific epithet. the combination is the name of the species. when writing the scientific name of an organism, it is proper to capitalise the first letter in the genus and put all of the specific epithet in lowercase. additionally, the entire term is ordinarily italicised (or underlined when italics are not available). the evolutionary relationships and heredity of a group of organisms is called its phylogeny. phylogenetic studies attempt to discover phylogenies. the basic approach is to use similarities based on shared inheritance to determine relationships. as an example, species of pereskia are trees or bushes with prominent leaves. they do not obviously resemble a typical leafless cactus such as an echinocactus. however, both pereskia and echinocactus have spines produced from areoles (highly specialised pad-like structures) suggesting that the two genera are indeed related. two cacti of very different appearancepereskia aculeataechinocactus grusoniialthough pereskia is a tree with leaves, it has spines and areoles like a more typical cactus, such as echinocactus. judging relationships based on shared characters requires care, since plants may resemble one another through convergent evolution in which characters have arisen independently. some euphorbias have leafless, rounded bodies adapted to water conservation similar to those of globular cacti, but characters such as the structure of their flowers make it clear that the two groups are not closely related. the cladistic method takes a systematic approach to characters, distinguishing between those that carry no information about shared evolutionary history – such as those evolved separately in different groups (homoplasies) or those left over from ancestors (plesiomorphies) – and derived characters, which have been passed down from innovations in a shared ancestor (apomorphies). only derived characters, such as the spine-producing areoles of cacti, provide evidence for descent from a common ancestor. the results of cladistic analyses are expressed as cladograms: tree-like diagrams showing the pattern of evolutionary branching and descent. from the 1990s onwards, the predominant approach to constructing phylogenies for living plants has been molecular phylogenetics, which uses molecular characters, particularly dna sequences, rather than morphological characters like the presence or absence of spines and areoles. the difference is that the genetic code itself is used to decide evolutionary relationships, instead of being used indirectly via the characters it gives rise to. clive stace describes this as having "direct access to the genetic basis of evolution." as a simple example, prior to the use of genetic evidence, fungi were thought either to be plants or to be more closely related to plants than animals. genetic evidence suggests that the true evolutionary relationship of multicelled organisms is as shown in the cladogram below – fungi are more closely related to animals than to plants. plants fungi animals in 1998, the angiosperm phylogeny group published a phylogeny for flowering plants based on an analysis of dna sequences from most families of flowering plants. as a result of this work, many questions, such as which families represent the earliest branches of angiosperms, have now been answered. investigating how plant species are related to each other allows botanists to better understand the process of evolution in plants. despite the study of model plants and increasing use of dna evidence, there is ongoing work and discussion among taxonomists about how best to classify plants into various taxa. technological developments such as computers and electron microscopes have greatly increased the level of detail studied and speed at which data can be analysed. symbols a few symbols are in current use in botany. a number of others are obsolete; for example, linnaeus used planetary symbols ⟨♂⟩ (mars) for biennial plants, ⟨♃⟩ (jupiter) for herbaceous perennials and ⟨♄⟩ (saturn) for woody perennials, based on the planets' orbital periods of 2, 12 and 30 years; and willd used ⟨♄⟩ (saturn) for neuter in addition to ⟨☿⟩ (mercury) for hermaphroditic. the following symbols are still used: ♀ female ♂ male ⚥ hermaphrodite/bisexual ⚲ vegetative (asexual) reproduction ◊ sex unknown ☉ annual ⚇ biennial ♾ perennial ☠ poisonous 🛈 further information × crossbred hybrid + grafted hybrid