Easily confused with : Over 400 other species of Holly, the majority external to the UK.
Hybridizes with : one of the 400 other Hollies to produce
Highclere Holly (Ilex × altaclerensis) which has wider flat oval leaves without cusps and either without prickles or with fewer prickly spines which all point forwards. Highclere Holly can have either red or pink berries. True Highclere Holly does not have variegated leaves, but garden varieties can be as they are further hybrids.
No relation to : New-Zealand Holly (which is an evergreen shrub with holly-like leaves but large daisy-like flowers and which does not belong to the Holly Family, but to the Daisy family). Nor does it have any relation to
Holly Oak an oak tree with holly-like leaves. Nor to
Holly-leaved Naiad, an aquatic plant. [All plants of similar names]
Uniquely identifiable characteristics
Distinguishing Feature : The heavily cusped dark green leaves with sharp prickly spines on the edges generally pointing radially away from the centre of the leaf. The cusped nature of the edges are caused by differential growth in the leaves: that nearer the edges grows more than that nearer the centre, causing the edges to warp.
The shape of Holly leaves varies from tree to tree and from place to place. The spines on the leaves of holly are fewer the higher up the tree the leaves are, because there is no need to defend those leaves with spines against herbivores which cannot reach them. There are not many lose giraffes in the UK. This characteristic was taken advantage of by horticulturalists to breed Holly trees lacking leaf-spines, such as in Highclere Holly shown above.
Hedgehog Holly is one variety that has been specially bred to have more spines. Holly trees grow more spines on the leaves as a result of browsing, and they accomplish this feat by modifying existing genes.
No relation to : Sea-Holly [a plant with similar name with similarly cusped and prickly leaves, but which are a totally different colour]
Holly is dioecious, meaning there are both both male and female plants, the male plants bearing male flowers, the female plants female flowers. The flowers are white with four petals. Only female plants produce berries, which must account for the high proportion of Holly trees/shrubs with no berries whatsoever.
Traditionally, Holly springs with red berries are used as Christmas decoration (rather than as Christmas Trees). In this regard, it shares popularity with Mistletoe. Holly was once used as an emetic, but it is poisonous. Holly contains Tannic Acid, the flavonols Rutin and Kaempferol, several triterpenoids (the bitter components) including α-amyrin and ursolic acid, anthocyanidins (the orange pelargonidin 3-bioside and the orange-red coloured (in acid conditions) cyanidin), and in the leaf only purine alkaloids (theobromine and caffeine). Theobromine is used to treat asthma.
The berries usually appear in Winter, before Christmas, when wreaths of holly sprigs bearing berries are used as Christmas decorations on front doors. But some hollies buck this trend: those growing along the Welsh Borders and around Shropshire produce berries months earlier in September. These trees belong to Europes oldest Holly grove with some having germinated at least 400 years ago (it was 2017 when this was written).
Cyanidin is an anthocyanidin, and is an orange-red pigment when in acidic conditions (pH <3), but as alkalinity increases, so does the colour change in progression. It is violet at the neutral pH of 7 and blue at pH > 11. It is found not only in the berries of Holly, but also in the fruits of |
Apples and also colours various vegetables such as red cabbage and red onion.
Red Cabbage water was once used as an indicator of pH. Like many anthocyanidins it is an anti-oxidant.
The berries are very toxic and in extreme cases can cause death. Ingestion of up to 5 berries will produce symptoms of poisoning, up to 30 berries can be fatal.
Menisdaurin is a toxic nitrile, or more precisely a Cyanogenic Glycosides, present at about 0.3% in the fruits (red berries).
Toxic Triterpenoids found in Holly and arranged in order. The successive rows show the Triterpenes α- and β-Amyrin, followed by the alcohol versions, the aldehyde versions and finally the acid versions. They were obviously named before the sequence was known of in Holly.
Ursolic Acid, which is cytotoxic, is present in many other plants including Bilberry, Cranberry,
Thyme, Apples and Prunes and also finds use in cosmetics.
Oleanolic Acid, is relatively non-toxic and is widely found in some edible plants including
Garlic being related to Betulinic Acid. It exhibits anti-tumour, anti-viral and liver protection properties.
Baurenol is another toxic triterpenoid found in Holly. Note that the major difference to the above series of inter-related triterpenoids is the position of the double bond.
A FLAVONOL GLYCOSIDE
Rutin, variously called rutoside or sophorin, is the disaccharide between the flavonol Quercetin and
rutinose which is found in the peel of number of citrus fruits, as well as berries such as those from, for instance, Holly, Cranberry and
Mulberry. It derives its name from
Common Rue (Ruta graveolens) where it was first found. It has a role within some plants conveying nutrients from soil to plant cells. It is useful as an anti-oxidant against the oxidation of iron Fe2+ in mammals who ingest it and as an anticoagulent for platelets in blood.
Theophylline, Caffeine and Theobromine (which contains no bromine) are purine base alkaloids (xanthine alkaloids, from the Greek 'Xanthos' (ςανφος), meaning yellow). They all contain 4 atoms of nitrogen; only the number and position if methyl groups changes. 'Theos' (Φεος) is Greek for 'God', Bromos (γρωμα) for food and 'Phyllon' (φυλλον) for leaf.
Some species of Holly contain significant quantities of Caffeine and Theobromine in the leaves, but apparently not Ilex Aquifolium. Theophylline, Caffeine and Theobromine (which contains no bromine) are purine alkaloids. They all contain 4 atoms of nitrogen; only the number and position if methyl groups changes.
Theobromine is found in cocoa (from the Cacao plant (Theobroma cacao)) (and therefore chocolate) and in Kola nuts and the tea plant and also in Ilex paraguariensis a species of Holly not native to the UK. Pharmacologically, Theobromine is used as a vasodilator, bronchodilator, a heart stimulant and a diuretic. It found use in the treatment of asthma.
Caffeine is a stronger CNS stimulant than Theobromine. Like theobromine, it too is a diuretic. Caffeine is found in the cherries of the Coffee Plant, the nuts of Kola and in the beans, fruits and leaves of some plants where it acts as a natural insecticide. Although Tea leaves contain more caffeine that coffee, less tea is used in the brewing of a cuppa and it therefore has less caffeine. The non-native Holly Ilex guayusa contains up to 4.5% caffeine. There is no resident theobromine in tea and very little theophylline, although caffeine does metabolise in the liver into 84% paraxanthine, 12% into theobromine and only 4% into theophylline. At sufficiently high doses caffeine is toxic, causing twitching, nervousness, irritability, anxiety, insomnia, tachycardia and arrhythmia. In yet higher doses manic depression, disorientation, hallucinations, psychosis and dissolution of muscle tissue can occur.
Theophylline was first discovered in Tea leaves, but its concentration therein is quite small. Like Caffeine and Theobromine it too is a diuretic and broncodilator and was found useful to treat asthma in the 1920's. Its presence in Holly is either non-existent, or too inconsequential to report and is shown here just for completeness' sake.
Xanthine itself is yellow, and shown here only to show its relationship to all three of the above-me purine alkaloids upon which they are based). Unlike the three former, Xanthine is devoid of any methyl group(s). It is found in plants and in mammals as a product of the metabolism of proteins and is found in urine. Containing so much nitrogen in relation to carbon, it is the bodys' way of disposing of excess nitrogen. [Xanthine should not be confused with the similar sounding
Xanthene (which does not contain nitrogen) and upon which many synthetic
Xanthene Dyes, such as
Fluorescein, are based].
Caffeic Acid has nothing whatsoever in common with Caffeine (shown above) as can be seen by the different chemical structure. It is ubiquitous, being present in all plants and a pre-requisite to the synthesis of lignin, the structural component of plants. In this regard it could have been placed under any heading. It acts as an anti-carcinogen and anti-oxidant, and the plant uses it as a very effective defence against any invading fungi. If eaten, it displays several beneficial effects against cancer and inflammation mediated by leukotrienes in various inflammatory responses.