Apiaceae
(Umbelliferae)
Alexanders (Smyrnium olusatrum)
Above: Alexanders (Smyrnium olusatrum). The size and color of a flower is tailored to its targetted pollinators. Small whitish or green flowers tend to appeal most to small beetles and flies. The problem is such small flowers may not easily catch the eyes of the small insects they are intended for. To counter this many plants group a number of small flowers together into arrays. A fairly loose array of flowers, each borne on its own stalk or pedicel or ray, forms a cluster called an umbel. Such umbels are characteristic of the Apiaceae or carrot family. This family includes some familiar culinary herbs: Carrot, Parsnip (of which the leaves are toxic and inedible), Celery, Fennel, Alexanders and Parsley, but other members are highly poisonous, such as Hemlock. The Apiaceae are a fascinating family displaying a range of interesting adaptations.
Umbels may themselves be grouped into compound umbels, as here, in which case the smaller secondary umbels are also called umbellules or umbellets. An involucre of bracts may surround the base of the main axis of the umbel and smaller bracts may occur at the base of the umbellule, in which case they form an involucel.
Click all photos to view full size.
Above: the young fruit of Alexanders (the fruit of this genus turn black when ripe). The fruit of the Apiaceae consists of a cremocarp -a dry dehiscent fruit that splits into a pair of indehiscent mericarps at maturity; the mericarps remaining attached to the carpophore (fruit stalk - specifically a forked structure that elongates as the fruit develops and from which the mericarps will be suspended). Note the pair of swollen style bases, the stylopodia (singular = stylopodium, literally style foot, a term used particularly when the base is swollen and distinct from the style or remaining attached to the fruit after styles are shed and is the roof formed over an inferior ovary). In the flower of Apiaceae these stylopodia secrete the nectar. The nectar is secreted through modified secretory stomata on the stylopodium surface.
The nectar can be seen to glisten on the stylopodia.
Apiaceae are most easily identified by their fruit. However,differences in the leaves and flowers are readily apparent. In some species the petals of individual flowers are all equal in length and the flowers are radially symmetric or actinomorphic. However, in some forms the outer petals on the outer flowers of the umbellules may be distinctly larger and the flowers are then zygomorphic, as in Heracleum.
The stem leaves are mostly biternate: compound leaves divided into 3 divisions, each division having 3 leaflets.The uppermost leaves tend to be ternate (uniternate) with 3 undivided leaflets. The lowermost leaves, particularly the radical leaves (those borne on the rootstock) have long stalks, are triternate with leaflets on stalks (that is divided into 3, with each division further divided into three with each secondary division bearing 3 leaflets). The leaves themselves are either divided or have crenate margins (as here). Such leaves are also termed decompound, that is compound leaves whose parts are also compound. Such divided compound leaves are typical of many Apiaceae.
The petioles (stalks) of the stem leaves (cauline leaves) each have a spathe-like sheath at the base.
Each umbel has between 3 and 15 rays up to 5 cm in length, from which each flower extends on a short stalk or pedicel. Individual flowers are only about 2 mm across. The young shoots and leaf stalks are edible and apparently taste like celery when raw.
Alexanders is found on cliffs, banks, by roads and ditches and in waste places, mainly near the sea.
Below: sea-holly (Eryngium maritimum)
Sea-Holly (Eryngium maritimum) has unusual inflorescences for Apiaceae: the simple umbel (i.e. not compound) consists of flowers very tightly compacted so as to be more correctly called a capitulum, as found in teasels (family Dipsacaceae) and the daisy family (Asteraceae). Each flower retains well-developed sepals (seen as five bluish, lanceolate structures with the midrib of each extending into a stout spine. The sepals are longer than the petals and persist in the fruit. Sea-Holly is perennial, with a creeping rootstock with a long, well-developed taproot and thick and fleshy rhizomes (stolons) extending from buried stems. The flowering stem reaches 15 to 60 cm in length, with the lower part often rootlike and buried in the sand.
Each flower is also surrounded by bracteoles (secondary bracts) which are spiny, tricuspidate and purplish-blue (click on photo and zoom in to see these). Each axis whether the main stem or a branch ends in an inflorescence in flowering individuals. The 5 petals are bluish-white and 3 to 4 mm long; the 5 stamens have purplish filaments and yellow anthers and there are 2 styles. The nectary forms a ring at the base of each flower (this is on top of the inferior ovary and corresponds to the stylopodia). There are 25 to 50 flowers per capitulum, most of them hermaphrodite.
The basal leaves are palmate, with thick prominent veins and thick cartilaginous margins with large spinose teeth and petioles about as long as the leaf-blade (lamina). The stem leaves are similar but lack petioles (they are sesile) and become progressively smaller towards the apex.Each capitulum is surrounded by 5-7 large, leaf-like and spiny bracts on the ends of each axis.
Sea-Holly, as the name suggests, is a maritime plant of sand and shingle. It is found in Europe, including the Mediterranean, northern Africa and the Middle East. It is a slightly succulent halophyte ('salt-lover') with xerophytic adaptations (adaptations to dry conditions, in this instance brought on by the dry, windy and salty maritime conditions). The plant secretes a thick layer of protective wax, accounting in part for the grey-blue color, along with anthocyanins in the bracts. The blue bracts and the compact flower heads serve to attract pollinating insects. Compaction of the tiny flowers may also give them some protection from drying-out.
The stomata, which occur in more-or-less equal numbers on both surfaces of the leaves, are sunken to reduce water-loss. Similarly, the epidermis on both leaf surfaces consists of two layers of thick-walled cells (collenchyme) and the leaves have 2-3 layers of photosynthetic palisade mesophyll beneath both surfaces.
The root and stem are protected by a well-developed (secondary) bark (with well-developed phelloderm) containing oil canals. The cortex of stem and root is very thick and both the cortex and medulla (pith) of the root is rich in oil canals. Many plants have oil canals, and indeed they are a characteristic of the mericarps of many Apiaceae, however, oil canals seem especially well-developed in many maritime plants. These essential oils generally have antimicrobial activity and may also discourage insect predators, but their additional development in maritime forms suggests additional functions that are not entirely clear. In fruit they may aid buoyancy.
The cremocarps of Sea-Holly do separate readily into pairs of cremocarps when ripe, but often each pair is dispersed as a single unit. There is no elongated and forked carpophore from which the mericarps hang as is the case for most Apiaceae. The fruit have moderate flotation abilities, able to survive floating on seawater for several days and occasionally as long as two weeks, facilitating occasional long-distance dispersal. However, shorter-range dispersal seems to be more important generally and is effected when the dry stems break at the end of the season, the dry plant becomes a 'tumbleweed' rolling along the beach scattering the fruit. Hooked bristles on the fruit, and the dry sepals that remain attached and well-developed oil glands all aid flotation. Each mericarp possesses 5 ridges typical of Apiaceae (3 dorsal and 2 lateral) and the two lateral ribs are well-developed with air-filled cells which must also aid flotation. (However, I suspect the hooks may also serve to catch the fur or feathers of seashore animals and so bring about animal-aided dispersal).
Further north in its range, Sea-Holly reproduces less effectively by seed and relies increasingly on vegetative propagation which occurs from rhizome offshoots and root fragments. Presumably the sea and shifting sand disperse these fragments.
Each year the rootstock puts out one or more basal leaves to form a basal rosette from which a flowering stem will later emerge. Flowering commences earlier in southern parts of the range: April/May in the Mediterranean and June to August in southern Britain. The plant dies back in Summer/Autumn. The terminal umbel flowers first and branches (paracladia, singular = paracladium: a repeating unit in an inflorescence) develop from the axils of bracts and these secondary axes also bear terminal umbels, which may go on to bear third-order flowering axes.
Further reading: Biological Flora of the British Isles - Eryngium maritimum.
Rock Samphire (Crithmum maritimum)
Rock Samphire or Sea Fennel (Crithmum maritimum) is the only recognised species of this genus. The flowers are yellow-green. It grows mostly on cliffs by the sea-shore, in hard to reach places, but can occasionally be found on sand or shingle. It is perennial, with a woody rootstock. The ascending stems may reach 15 to 30 cm. The involucre and involucels consist of a ring of small ovate to triangular leaves and the umbels have 8 to 20 rays. The leaves are pinnate, with two pairs of lateral leaflets, or ternate with ternate or biternate leaflets. The segments of the leaflets are fleshy - a halophytic adaptation to maritime conditions with dry salty winds. The cremocarp separates into a pair of indehiscent mericarps each of which has a thick coat of spongy tissue that allows the fruit to float on the sea for a considerable length of time, aiding dispersal, and also sequester salt, preventing the salt from reaching the embryo contained in the seed within (the seed having a much reduced seed coat or testa).
Crithmum maritimum occurs in parts of Europe, such as along rocky Mediterranean coasts and the white chalk cliffs of Kent in the British Isles. Once prized as a delicacy, especially when pickled, it is now protected in Britain.
Fennel (Foeniculum vulgare)
Foeniculum vulgare has bright yellow flowers in which the petals do not fully unfurl but are partially rolled upwards from tip to base, a condition sometimes described as involute but better described as circinate. Click on the image above to see the full size and zoom in to see this. The umbels have no bracts or bracteoles. The fruits (cremocarps) are oval with ridges. The leaves are edible (taste of aniseed) and the fruits are particularly nutritious and this plant has a long history of cultivation. In Britain, it is considered native along coasts but inland forms are probably escapees from cultivation. Often found on waste ground and especially on banks and cliffs near the sea.
The leaves of Fennel are 3 or 4 times pinnate with capillary-like segments that are oriented in three dimensions rather than being in one plane.
Fennel is a large perennial, to 2.5 m, seen growing with Teasel above.
The petioles (leaf stalks) are dilated and amplexicaul (surround the stem). The stems are initially solid but become hollow in places. Dill, Anethum graveolens, is similar but only reaches about 60 cm in height and has a completely hollow stem, but with similar leaves and flowers but the main difference is in the fruits, which are flattened and winged in Dill.
Hog's fennel (Peucedanum officinale)
Also known as Sea Hog's Fennel and Sulphur-wort, Hog's Fennel has leaves that are three to five-times ternate (up to 6-times ternate according to some sources) and is a large perennial, superficially similar to Fennel and reaching 2 m in height. It is native to Britain, though very local in parts of E Kent (Faversham and Whitstable) N Essex and E Suffolk but is also native to other parts of western Europe (except northern regions) including the Mediterranean region. It occurs on rough brackish grassland and near paths by the sea.
The fruit are elliptical-oval, with 5 ridge, and compressed
Hogweed (Heracleum sphondylium)
Hogweed (Heracleum sphondylium)or Common Cow-Parsnip is found in hedges, open places, woods, moist meadows and similar places and mountain areas and is very common. It is distributed across most of Europe, parts of Asian and northern Africa.
The compound umbels are large and the outermost flowers are zygomorphic and radiant (radiant means the petals form elongated rays radiating outwards from the center) in subspecies sphondylium or greenish, actinormorphic and non-radiant in ssp. sibiricum. The flowers are protandrous (male parts ripen first with female parts ripening when the male parts have completed their function) to encourage cross-pollination. Most of the flowers are hermaphroditic, but male flowers (with aborted female parts) also occur, particularly in umbels borne on tertiary branches).
It is sometimes assumed that with their simple flowers with open nectaries that Apiaceae are generalists, being visited and pollinated by a wide range of insects. However, studies in Heracleum have shown that although many insects, especially flies, hoverflies and beetles visit these flowers, only a few species act as efficient pollinators. Furthermore, different species of Heracleum utilise largely different pollinators which are selecting pollen on the basis of size, resulting in very little hybridisation. The green-flowered form of Hogweed and the white-flowered form also attract and utilise a different, but overlapping, set of pollinators.
The leaves are very variable but are generally ternately pinnate: that is compound leaves divided into three main leaflets that are themselves pinnate: two lateral leaflets on long stalks and a terminal leaflet cleft into three lobes.
Above a fruit (cremocarp) of Heracleum sphondylium. The fruit of Apiaceae consists of a cremocarp, a double unit which usually splits into two separate mericarps (achenia) when ripe, with the mericarps suspended from the columella (carpophore or 'fruit stalk') which may also split partially into two. Each mericarp usually has 5 main or primary ridges (ribs) and 4 secondary ones. Dark-colored resin canals called vitae are usually present embedded in the fruit wall but visible externally. The vitae contain essential oils. The bases or feet of the styles (sylopodia) typically remain as a pair of 'horns'.
As the fruit ripen or dry the features become more apparent. Note the 3 filiform dorsal ribs towards the midline (2 lateral ribs are also present but these are harder to see). There is a thin outer wing around the perimeter of each mericarp. Note that 4 resin canals (vitae) are visible on the back of each mericarp (the two mericarps still fused front-to-front in this unripe fruit). The two inner vitae are the dorsal vitae and the outer pair are the lateral vitae. The lateral pair is especially thickened at the apex and club-shaped, the inner pair may be linear or club-shaped (here they are slightly club-shaped). The commissure (the face we can not see here joining to the carpophore, facing the other mericarp) also has two vitae that are generally club-shaped.
Above: a ripe mericarp, separated from its partner, showing the outer convex face with resin glands, ribs and the peripheral wing. Below: the inner (commissurial) concave face of the same mericarp with a single pair of resin canals and a single median rib. The scar where the fruit was attached to the carpophore can be seen at the top.
Below: these features are consistent - my sample of 15 mericarps all have the same arrangement of ribs and resin ducts, making these features diagnostic of the species.
Resin ducts in the fruit of some plants have been shown to protect the seeds from insect predation and to have antimicrobial (including antifungal) properties.
